IS18591-2024 Geosynthetic Reinforced Soil Structures — Code of Practice

IS 18591 : 2024
भुकृत्रिम प्रबत्रित मृदा संरचनाएँ — रीत्रत
संत्रिता
Geosynthetic Reinforced Soil
Structures — Code of Practice
ICS 93.020; 59.080.70
 BIS 2024
भारतीय मानक ब्यूरो
BUREAU OF INDIAN STANDARDS
मानक भवन, 9 बिादुर शाि ज़फर मार्ग, नई त्रदल्िी - 110002
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI - 110002
www.bis.gov.in www.standardsbis.in
May2024 ₹ 2390
भारतीय मानक
,QGLDQ6WDQGDUG
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Geosynthetics Sectional Committee, TXD 30
FOREWORD
This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Geosynthetics
Sectional Committee had been approved by the Textiles Division Council.
Soils, one of the most widely used materials in civil engineering, is weak in tension. The tensile strength, shear
strength and stiffness of soils can be improved by reinforcing the soils with tensile inclusions. The technique of
soil reinforcement is greatly useful in engineering efficient, economical and sustainable solutions for diverse
applications in several areas of application like earth retaining structures, slope stabilization, ground improvement
etc. Reinforced soil retaining structures have been extensively used in India over the last twenty-five years in the
highways to retain approaches to flyovers, underpasses and over bridges and also in residential and commercial
development projects. A significant number of reinforced soil slopes have been used in hill roads, airports and
residential and commercial development projects. A limited number of reinforced soil true abutments and shored
reinforced soil structures have also been constructed in India and, most likely, the demand for these structures
may increase in the future. The technique of basal reinforcement is a popular method for improving the stability
of embankments constructed on poor ground.
The need to explore more sustainable alternatives to conventional solutions is becoming increasingly important
and urgent in view of the demands of rapid growth in infrastructure and residential, commercial and industrial
development coupled with the increasing shortage of traditional construction materials like aggregates, sand and
earth. At the same time, a wide range of world-class soil reinforcement materials, including geogrids, geo-strips,
geotextiles and geocells are being manufactured in India. Extensive use of appropriate reinforced soil technology
can significantly contribute to the efficient development of infrastructure and constructed facilities meeting the
requirements of performance, economy and sustainability. To ensure the safety, serviceability and durability of
reinforced soil structures, comprehensive and authoritative guidance covering all relevant aspects, including
materials, design and construction, is required.
Reinforced soil walls and slopes may comprise a wide range of polymeric or metallic soil reinforcements, facings
and fills and may be used for diverse applications, including retaining the bridge approaches, highway grade
separators, embankments, hill roads, site grading, landscaping etc. Reinforced soil true abutments support the
bridge/viaduct deck in addition to retaining the earth. Shored reinforced soil walls/slopes, which combine the
technique of soil reinforcement with in-situ shoring techniques like soil nailing, are very useful for the construction
of roads and site development in hilly terrains. Basal reinforcement and basal mattresses could be used to improve
the stability of embankments and other earth structures constructed on poor ground.
Reinforced soil walls and slopes are very cost-effective which explains why the concept has emerged as one of
the most exciting and innovative civil engineering technologies in recent times.
This code of practice covers investigations, material specifications, design, detailing and construction of the
following types of reinforced soil structures — reinforced soil walls, reinforced soil slopes, reinforced soil true
abutments, shored reinforced soil walls/slopes and embankments with basal reinforcement/mattress. It provides
comprehensive and detailed guidance to enable engineers to design and construct reinforced soil structures that
are safe, serviceable and durable. The reinforced soil structures covered by this standard, provide an energy
efficient and cost saving alternative to similar structures built in reinforced concrete (RCC) or stone masonry.
The publishing of standard was possible, as over the last decade and a half, India acquired an in house experience
of design and construction of constructing several hundreds of major and important reinforced soil structures
replacing RCC and masonry structures. It must also be mentioned here, that the said reinforced soil structures
were constructed by using indigenously manufactured reinforcement systems backed by centres equipped with
advanced testing of reinforcements and other materials and products needed to construct reinforced soil structures.
Reinforced soil structures when compared with RCC structures at equivalent performance consume significantly
less quantity of cement and steel and therefore provide a fossil energy efficient structural system.
(Continued on third cover)
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CONTENTS
SECTION 1 GENERAL PAGE
1 SCOPE
2 REFERENCES
3 TERMINOLOGY
4 SYMBOLS
5 BASIC CONCEPTS OF SOIL REINFORCEMENT
6 REINFORCED SOIL STRUCTURES
7 DESIGN PHILOSOPHY
8 CLASSIFICATION OF REINFORCEMENT
9 REINFORCED SOIL STRUCTURES NOT INCLUDED IN THE SCOPE OF THIS CODE
10 REINFORCED SOIL STRUCTURES WHICH MAY NEED ADDITIONAL ANALYSIS
AND CHECKS
11 ORGANIZATION OF THE CODE
1
SECTION 2 SUBSURFACE INVESTIGATIONS
12 INTRODUCTION
13 GEOTECHNICAL CATEGORIES
14 INFORMATION REQUIRED FROM THE SUBSURFACE INVESTIGATIONS
15 COMPONENTS OF THE SUBSURFACE INVESTIGATION PROGRAMME
16 INFORMATION REQUISITES TO PLANNING AN INVESTIGATION
17 PLANNING, DESIGN AND EXECUTION OF THE SUBSURFACE INVESTIGATION
PROGRAMME
18 EXPLORATION METHODS
19 NUMBER, LOCATION AND SPACING OF BOREHOLES
20 DEPTH OF EXPLORATION
21 SELECTION OF TYPE OF TEST
22 BORING AND SAMPLING
23 LABORATORY TESTS
24 THE REPORT
SECTION 3 MATERIALS
25 SCOPE
26 FILL MATERIAL
27 REINFORCEMENT MATERIALS
28 POLYMERIC DRAINAGE PRODUCTS
29 OTHER POLYMERIC PRODUCTS
30 OTHER MATERIALS
1
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5
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8
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26
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SECTION 4 DESIGN OF REINFORCED SOIL WALLS
31 SCOPE
32 GENERAL
33 REINFORCED SOIL WALL ELEMENTS AND MATERIALS PROPERTIES
34 DESIGN
35 DESIGN FOR EXTREME EVENTS
36 DESIGN CONSIDERATIONS FOR COMPLEX GEOMETRIES
37 WATER FRONT REINFORCED SOIL WALL STRUCTURES
38 GROUND IMPROVEMENT
39 PANEL REINFORCEMENT DESIGN
SECTION 5 DESIGN OF REINFORCED SOIL SLOPES
40 GENERAL
41 APPLICATION OF REINFORCED SOIL SLOPES
42 MATERIALS
43 DESIGN
44 DETAILING
45 CONSTRUCTION AND MAINTENANCE
SECTION 6 DESIGN OF REINFORCED SOIL TRUE ABUTMENTS
46 INTRODUCTION
47 SCOPE
48 TYPES OF RS ABUTMENTS, COMPONENTS AND MATERIAL PROPERTIES
49 SOIL PROPERTIES
50 DESIGN PRINCIPLES
51 IMPORTANT POINTS TO BE KEPT IN MIND DURING RS ABUTMENT DESIGN
52 PROVISION OF CONSTRUCTION JOINT
53 BRIDGE ABUTMENT TYPICAL LAYOUT PLAN
54 CONSTRUCTION SEQUENCE FOR BRIDGE ABUTMENT
SECTION 7 DESIGN OF SHORED REINFORCED SOIL STRUCTURE
55 INTRODUCTION
57 SRS WALL DESIGN CONSIDERATIONS
58 REINFORCEMENT LENGTH
59 INTERFACE CONNECTIONS BETWEEN RS WALL REINFORCEMENTS AND
SHORING WALL OF SRS SYSTEM
60 GEOMETRY OF RS/SHORING INTERFACE
28
28
29
32
66
72
74
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79
79
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81
81
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119
iv
56 EVALUATION OF SHORED STRUCTURE SUITABILITY : PRE-DECISION
EVALUATION STUDIES
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61 DRAINAGE CONSIDERATIONS OF SRS WALL
62 DESIGN OF RS WALL COMPONENT OF AN SRS WALL SYSTEM
SECTION 8 DESIGN OF BASAL REINFORCEMENT
63 INTRODUCTION
64 DESIGN OF BASAL REINFORCED EMBANKMENTS OVER SOFT SUBSOILSRS
WALL DESIGN CONSIDERATIONS
65 EMBANKMENTS OVER VOIDS
66 BASAL MATTRESS REINFORCED EMBANKMENTS
67 STABILITY ANALYSIS OF EMBANKMENTS WITH HDPE GEOCELLS AS BASAL
REINFORCEMENTS
68 STABILITY IN THE DIRECTION ALONG THE EMBANKMENT
69 ALLOWABLE STRAIN IN REINFORCEMENT
70 MULTIPLE REINFORCEMENT BASAL LAYERS
71 FOUNDATION SETTLEMENT
72 BASAL REINFORCED EMBANKMENTS WITH VERTICAL DRAINS
SECTION 9 DRAINAGE DETAILING
73 INTRODUCTION
74 SITE CONDITIONS REQUIRING DRAINAGE
75 OVERVIEW OF REINFORCED SOIL RETAINING STRUCTURE DRAINAGE
FEATURES
76 MONSOON PREPARATION AND PLANNING
77 MAINTENANCE OF DRAINAGE
SECTION 10 DETAILING AND CONSTRUCTION ASPECTS
78 SCOPE
79 DESIGN DETAILING
80 CONSTRUCTION
81 RELEVANT POINTS TO BE INCORPORATED IN CONSTRUCTION DRAWINGS
82 SALIENT POINTS
ANNEX A REFERENCES
ANNEX B TERMINOLOGY
ANNEX C SYMBOLS
ANNEX D BORE/PIT LOG AND SOIL TEST DATA SUMMARY
ANNEX E COMMITTEE COMPOSITION
120
120
126
127
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144
144
144
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151
168
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200
202
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GEOSYNTHETIC REINFORCED SOIL STRUCTURES —
CODE OF PRACTICE
SECTION 1 GENERAL
1 SCOPE
This code covers the design and construction of the
following types of reinforced soil structures:
a) Reinforced soil walls;
b) Reinforced soil slopes;
c) Reinforced soil true abutments;
d) Shored reinforced soil walls/slopes; and
e) Basal reinforced embankments on soft
soils.
2 REFERENCES
The standards listed in Annex A contain provisions
which through reference in this text, constitute
provisions of this standard. At the time of
publication, the editions indicated were valid. All
standards are subject to revision and parties to
agreements based on this standard are encouraged to
investigate the possibility of applying the most
recent edition of these standards.
3 TERMINOLOGY
For the purpose of this standard, definitions given in
Annex B shall apply.
4 SYMBOLS
For the purpose of this standard, the letter symbols
given in Annex C shall have the meaning indicated
against each; where other symbols are used, they are
explained at the appropriate place.
5 BASIC CONCEPTS OF SOIL REINFORCEMENT
5.1 Soil reinforcement is the technique of improving
the strength and/or stiffness of soils and other fills
with tensile inclusions. Soils have high compressive
strength when confined but have low tensile strength
and shear strength of soils depend on effective
confining stresses. Reinforcement with tensile
inclusions enables soils to resist tensile stresses and
increases the shear strength and stiffness of soils.
5.2 Soil reinforcement may be employed to
construct select fills at steeper slope angles or to
improve the load bearing capacity of fills or the
ground. The applications of soil reinforcement may
be classified into three broad categories – reinforced
soil retaining walls and bridge abutments, reinforced
soil slopes and reinforced soil foundations.
5.3 Materials for soil reinforcement include metallic
strips, grids and meshes and geosynthetics –
geogrids, geotextiles and geo-strips. Important
characteristics of reinforcement are long term tensile
strength, interface shear properties and appropriate
connection system to facing.
6.1 The following types of reinforced soil structures
are covered by this code:
a) Reinforced soil walls;
b) Reinforced soil slopes;
c) Reinforced soil true abutments;
d) Shored reinforced soil walls/slopes; and
e) Basal reinforcement for embankments.
6.2 Reinforced soil walls as in (a) above, are
internally stabilized earth retaining structures with a
face inclination equal to or more than 70 to the
horizontal, in which the reinforcements are placed in
an approximate horizontal direction, between
successive lifts of fill during construction as a result
the reinforced fill behaves as a coherent mass.
6.3 Reinforced soil slopes as in (b) above, are
internally stabilized earth structures with a face
inclination less than 70 to the horizontal, in which
the reinforcements are placed in an approximate
horizontal direction, between successive lifts of fill
during construction and the reinforced fill behaves
as a coherent mass.
6.4 Reinforced soil true abutments, as in (c) above
are reinforced soil walls in which in addition to
retaining earth, the reinforced fill supports a bridge
or viaduct superstructure, which transmits relatively
large vertical and horizontal forces to the reinforced
fill through a footing, which is directly placed on the
reinforced fill.
6.5 Shored reinforced soil walls/slopes, as in (d)
above are a special type of reinforced soil structure
with relatively short length reinforcements and in
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which the retained zone behind the reinforced fill
(which may be natural ground or fill retained by an
existing reinforced soil structure/retaining wall) is
shored or stabilized using nailing, ground anchors or
embedded retaining walls, prior to the construction
of the reinforced soil wall/slope. The shored retained
zone does not exert any destabilizing forces on the
reinforced soil wall/slope.
6.6 Basal reinforced embankments are earthen
embankments constructed on soft soils in which the
stability of the embankment is enhanced by placing
at its base one or more layers of reinforcements or a
mattress across the full width or extending on either
side.
7 DESIGN PHILOSOPHY
7.1 A load and resistance factor (LRFD) design
approach is followed for the design of reinforced soil
walls and true abutments. The disturbing forces are
increased by applying load factors and the resisting
forces are reduced by applying resistance factors.
The ratio of the factored resistance to the factored
load is defined as the capacity demand ratio (CDR).
A structure is stable if the value of CDR is greater
than or equal to 1. Stability and service ability are
checked for the relevant load combinations.
7.2 Limit state or load and resistance factor approach
have not extensively been used for the analysis and
design of slopes. Hence in this standard, an
allowable stress design (ASD) approach is adopted
for the design of reinforced soil slopes. Stability
analysis is carried out considering unfactored loads
and resisting forces and an acceptable margin
against failure is ensured through the use of an
overall factor of safety. Analysis and design of
reinforced soil slopes is usually carried out using
commercially available software.
7.3 The design procedure for shored reinforced soil
walls and slopes considers the stabilizing effect of
the shoring wall on the long-term stability of the
reinforced soil wall/slope mass. A LRFD approach
is adopted for the design of shored reinforced soil
walls and an ASD approach is recommended for
shored reinforced soil slopes.
7.4 An allowable stress design (ASD) approach is
adopted for the design of embankments on soft soils.
Additional ground improvement measures such as
the piles, stone columns, sand drains etc. may also
have to be employed are not covered by this code.
8 CLASSIFICATION OF REINFORCEMENT
8.1 In terms of the load versus elongation
characteristics of the reinforcement namely the
stress-strain characteristics of the fill, reinforcements
are classified as inextensible or extensible.
Inextensible reinforcements mobilize their design
resistance at strains appreciably less than the failure
strain of soils. Extensible reinforcements mobilize
their design resistance at strains comparable to the
failure strain of soils. There are some significant
differences in the behaviour of structures reinforced
with inextensible and extensible reinforcements,
which are reflected in the design methods.
8.2 In this code, the following types of
reinforcements are considered as inextensible:
a) Metallic strips;
b) Metallic welded wire grids and bar mats;
and
c) Polymeric strips provided sufficient data is
available to prove the design approach.
8.3 The following types of reinforcements are
considered as extensible:
a) All geosynthetic (polymeric) reinforcements
including geogrids, woven geotextiles,
geostrips and geocells; and
b) Hexagonally woven double twisted steel
wire mesh.
9 REINFORCED SOIL STRUCTURES NOT
INCLUDED IN THE SCOPE OF THIS CODE
The following types of reinforced soil structures are
not included in the scope of this code:
a) Reinforced soil structure comprising a
reinforced soil wall in the lower part and a
reinforced soil slope with face inclination
greater than the angle of shearing resistance
of the fill in the upper part;
b) Anchored earth or multi-anchored
structures, wherein fills are reinforced with
metallic bars or strips with an anchor
mobilizing passive resistance at the end.
Though such structures have many
similarities with reinforced soil structures,
they may have significant differences also
and are not covered by this code; and
c) Design for applications like soil
reinforcement below structural
footings/rafts, load transfer platforms, hard
standages and within the pavements,
railway track beds, etc, are not covered by
this code.
WHICH MAY NEED ADDITIONAL
ANALYSIS AND CHECKS
10.1 The recommendations on materials, design,
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construction, drainage and detailing presented in this
code are applicable for reinforced soil structures
used for different applications. However, in some
instances, the procedures given in this code may not
be sufficient for the complete design of the
reinforced soil structures and additional analyses,
detailing and treatments may be required to ensure
the safety, serviceability and durability of the
structure. Examples of such structures include:
a) Tall reinforced soil structures (reinforced
soil walls with height greater than 15 m and
reinforced soil slopes with height greater
than 30 m): In some cases, it may be
required to consider aspects like the
compressibility of fill, compressibility of
facing and their effects on connections. It
may be required to supplement the design
calculations recommended in this code
with more advanced numerical analysis
techniques like finite element or finite
difference methods;
b) Reinforced soil structures with more than
two tiers; and
c) Reinforced soil structures retaining water
or exposed to water bodies: Although some
guidance is given in Section 4, the effects
of submergence, seepage, sudden draw
down, internal erosion and piping, scour,
flow velocity, current velocity, abrasive
forces, and cyclic waves etc need particular
attention with respect to material
specifications, design, detailing,
construction and monitoring.
10.2 It should be noted that provisions in this code
are applicable for typical situations. It may therefore
not be adequate to directly adopt the same in the case
of ‘a typical’ situations arising out of geometry,
loading and field conditions, which need to be
carefully investigated, analysed and designed.
11 ORGANIZATION OF THE CODE
This code comprises 10 sections. Section 1 defines
the scope, terminology and symbols and presents a
brief outline of the basic concepts, design
philosophy and some of the limitations of this code.
Section 2 provides recommendations on
geotechnical and geophysical investigations and
testing. Section 3 pertains to the materials including
reinforcement, facing, fill and drainage. Section 4
covers the design of reinforced soil walls
with a normal retaining function including
recommendations on the design of structures with a
complex geometry and waterfront structures.
Section 5 presents the design and detailing of
reinforced soil slopes. Section 6 pertains to the
design of reinforced soil true abutments and
Section 7 provides recommendations on the design
of shored reinforced soil structures. Section 8 covers
the design of embankments on poor ground
stabilized with basal reinforcement or basal
mattress. Section 9 provides recommendations on
the drainage of reinforced soil structures. Section 10
presents recommendations on the detailing and
construction of reinforced soil structures.
SECTION 2
SUBSURFACE INVESTIGATIONS
12 INTRODUCTION
12.1 This chapter provides requirements related to
subsurface investigations for reinforced soil
structures, including the planning and reporting of
subsurface investigations and general requirements
for commonly adopted field and laboratory tests.
12.2 The objectives of subsurface investigations for
reinforced soil structures include:
a) To obtain data on subsurface conditions at
the location of the reinforced soil structures
for evaluation of stability and serviceability
of the reinforced soil structures, including
lateral sliding, bearing capacity, lateral
extrusion, global stability, liquefaction,
ground subsidence, settlement, and
drainage. At select locations, data on
subsurface conditions may be required in a
direction perpendicular to the alignment of
the reinforced soil structures, for example,
for global stability analysis;
b) To obtain data on subsurface conditions at
for the design and monitoring of ground
improvement;
c) To obtain data on subsurface conditions at
for assessment of construction problems
and difficulties; and
d) To identify potential, borrow areas of fill
materials and to assess the geotechnical and
chemical characteristics as well as quantity
of fill materials.
12.3 The subsurface investigations shall be carried
out by personnel with specialized knowledge and
experience of fieldwork and laboratory testing.
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A qualified and experienced geotechnical engineer
shall prepare the geotechnical investigation report.
13 GEOTECHNICAL CATEGORIES
For analysis purposes, reinforced soil structures are
geotechnically categorized as follows:
a) Geotechnical Category A — These
structures include:
1) Conventional reinforced soil ramps –
walls or slopes; and
2) Reinforced soil slope embankments
and earth structures
b) Geotechnical Category B — These are
reinforced soil structures that fall outside
the conventional indicated as Category A,
such as:
1) True abutments;
2) Shored reinforced soil structure;
3) Reinforced soil structures with height
greater than 10 m;
4) Reinforced soil structures with
foundations requiring ground
improvement;
5) Reinforced soil systems involving
abnormal risks, complex profiles,
unusual or exceptionally subsoil
conditions, or difficult loading
conditions;
6) Systems in highly seismic zones
(Zone 4 and Zone 5); and
7) Systems in probable areas of scour,
areas subjected to flooding and
sudden drawdown, site instability, or
persistent ground movements for any
reason.
Subsurface investigations for geotechnical
Category A structures shall require standard
detailed geotechnical investigations. Geotechnical
Category B structures shall require additional
investigations necessary to those circumstances that
classify the structure and its components under that
category.
14 INFORMATION REQUIRED FROM THE
SUBSURFACE INVESTIGATIONS
The important information required from the
subsurface investigation programme includes the
following:
a) The sequence, depth, thickness of
subsurface strata at the location of the
reinforced soil structures;
b) The type/classification of each
subsurface stratum at the location of
c) Geotechnical design parameters
for subsurface strata including
drained/undrained shear strength
parameters, deformation modulus,
consolidation characteristics,
permeability, liquefaction potential;
d) The depth of groundwater table and its
seasonal variations;
e) The availability and volume of suitable
fill materials and their characteristics
including grain size distribution, grain
shape, atterberg limits, shear strength
parameters, compaction characteristics,
chemical characteristics (resistivity, pH,
chloride content);
f) Information on underground utilities
and obstructions which may cause
difficulties in the construction of
reinforced soil structures or which may
be affected or damaged by the
construction of reinforced soil
structures; and
g) Any other specific subsurface features
which may pose a risk to the
safety, serviceability, durability and
constructability of the reinforced soil
structure.
15 COMPONENTS OF THE SUBSURFACE
INVESTIGATION PROGRAMME
The major components of the subsurface
investigation programme include the following:
15.1 Desk Study
15.2 Site Reconnaissance/Walkover Survey
15.3 Geological Mapping
15.3.1 Test Pits
Test pits are suitable for sites where rock is
encountered at shallow depths. Representative and
undisturbed soil samples could be collected
from test pits. Test pits are also suitable for visual
This includes a review of available information on
local geology and geotechnical data at nearby
locations. The information will be greatly useful in
planning the extent of investigations and selecting
the appropriate method of investigation and
selection of appropriate field tests and sampling.
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inspection of subsurface strata and verifying the
presence of utilities and other underground features.
15.3.2 Soundings
Static cone penetration test (SCPT) is suitable in
sedimentary deposits like sands, clays and silts.
SCPT is generally not suitable in dense gravels,
boulders, residual soils, IGMs and rocks.
15.3.3 Boreholes
Boreholes are suitable in most ground conditions
and facilitate exploration up to large depths and
facilitate collection of representative and
undisturbed samples of soils and rock cores and
conducting of field tests at different depths.
Boreholes also allow determination of ground water
levels and collection of ground water samples.
15.3.4 Field Tests in Boreholes
Field tests are conducted at regular intervals at
different depths in boreholes. Field tests include:
Standard penetration test (SPT), field vane shear test
(FVST) and pressure meter test (PMT).
15.3.5 Geophysical Tests
The geophysical investigations shall be conducted as
a supplement to the geotechnical investigation in
major projects.
15.3.6 Laboratory Tests on Soil, Rock and Ground
Water Samples — Laboratory tests include:
a) Tests on representative soil samples of
foundation strata (SPT samples from
borehole, bulk samples from test pits) for
determination of grain size distribution,
Atterberg limits, specific gravity, organic
content;
b) Tests on undisturbed soil samples from
foundation strata (usually thin-walled tube
samples from medium stiff to very stiff
clay/silt strata) for determination of shear
strength and consolidation characteristics;
c) Tests on rock cores from foundation strata
for determination of porosity, uniaxial
compressive strength (soaked and
unsoaked), point load index (soaked and
unsoaked). Usually coring in rock and tests
on rock cores will be required only in cases
where the rock is encountered at less than
10 m depth below GL;
d) Tests on representative soil samples of fill
materials (usually bulk samples from
test pits, but may include samples from
boreholes in some cases) for determination
of grain size distribution, grain shape,
Atterberg limits, specific gravity, organic
content, compaction characteristics, shear
strength characteristics, permeability, swell
characteristics, chemical characteristics
including resistivity, pH and chloride
content; and
e) Tests on groundwater samples may be
required in some cases (for example, where
groundwater may flow into hillside
reinforced soil structures) to determine
resistivity, pH and chloride content.
16 INFORMATION REQUISITES TO
PLANNING AN INVESTIGATION
The information from project inputs, preliminary
desk studies, and site reconnaissance shall be
reviewed before planning an investigation.
16.1 Project Inputs
The geotechnical category of the structure shall be
determined. Due consideration shall be given to
various aspects and requirements of the project on
which geotechnical factors will have an impact,
minor or major.
16.2 Preliminary Desk Studies for the Feasibility
Phase of the Project
Prior to the first site visit or chalking out the first
subsurface investigation program, initial desk
studies shall be carried out to collect necessary
general information, including:
a) Seismicity of the region within which the
project site is located;
b) Topography maps of the region to a scale
amenable for study;
c) Records of high-water levels, flood levels,
and other hydrological data;
d) Erosion and scour data for the adjoining
river(s), if any;
e) Landslides, subsidence etc in the region;
f) Any geotechnical phenomena peculiar to
the region, including the presence of
expansive soils, chemical content of sub-
soil and/or groundwater that could be
harmful to geosynthetics, concrete or
reinforcement steel;
g) Subsurface investigation reports for the site
if conducted in the past or reports for sites
in the vicinity;
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h) Construction records of sites in the vicinity,
including the following information:
1) Type of foundations adopted;
2) Load-carrying capacities considered;
3) Deformations of the foundations, if
any observed and recorded;
4) Groundwater encountered and how it
was tackled during deep excavations;
5) Issues related to expansive soils;
6) Distresses in the constructed structure,
if any; and
7) Any problems/issues encountered
during construction.
j) Underground obstacles that can hamper
geotechnical investigations, including
water supply lines, sewer lines,
drainage systems, buried electrical/
optic fibre/telecommunication cables, an
above-ground structure such as overhead
transmission lines requiring safe clearances
etc;
k) Any changes expected in the course and
profile of a stream nearby;
m) Availability of water at the site, including
the adequacy of borewells; and
n) Logistics to the site to bring equipment
from the nearest rail head and approach
roads. Also, consider the need to make
temporary unpaved roads to facilitate
equipment movement to various test
locations.
NOTE — The above information may be available
with Survey of India, Geological Survey of India,
local authorities, including the collector’s office, the
local PWD and Gram Panchayats. Further
information may be obtained from the locals and
agriculturists residing in the locality.
16.3 Site Reconnaissance
Information obtained from preliminary desk studies
shall be confirmed by a site reconnaissance. The
following points shall be noted during the
reconnaissance:
a) The local topography of the site;
b) Obstructions above the ground and below
the ground, including culverts, etc;
c) The nature of the vegetation, including the
types of crops cultivated, which can reflect
upon the soil type, ground moisture
conditions, water table etc;
d) Access to the site locations;
e) Trial pits and hand auger details that would
give some details of the upper regions of
the sub-surface;
f) Any outstanding geological features such
as ravines, faults, escarpments, flow
patterns on a macroscopic scale of
adjoining river, stream etc;
g) Evidence of landslides and a visual review
of slope stability in hilly terrain by an
expert eye;
h) Water levels in streams and river traversing
at/near the site, including seasonal
fluctuations, high flood marks, etc;
j) Evidence of changes in flow patterns of
watercourses;
k) Groundwater levels as observed from local
open wells and seasonal fluctuations as
obtained from local inquiries;
m) Behaviour of existing structures, including
bridges and culverts, their subsoil and
foundation details, foundation types, their
load-carrying capacities, construction
problems, if any, scour issues, river
training works, etc; and
n) Inquiries for sources of supply of water and
electric power during investigations.
17 PLANNING, DESIGN AND EXECUTION
OF THE SUBSURFACE INVESTIGATION
PROGRAMME
17.1 The key elements in the planning and design of
the subsurface investigation program include the
following:
a) The number, location and depth of
boreholes, soundings (SCPT) and test pits
along the alignment and perpendicular to
the alignment of the reinforced soil
structures;
b) The type and number (frequency) of field
tests to be conducted in boreholes for
various types of strata;
c) The type and number of undisturbed
samples to be collected from boreholes;
d) The laboratory test program for soil, rock
and groundwater samples from foundation
strata;
e) The type, spacing and depth of geophysical
investigations along the alignment and
perpendicular to the alignment of the
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f) The scope of geological mapping to be
carried out by geologist;
g) The number, location and depth of test pits
and boreholes (where applicable) in borrow
areas and laboratory test programme for fill
materials; and
h) The information to be included in the
factual and interpretative reports for
geological, geotechnical and geophysical
investigation reports.
17.2 The above key elements should be finalized on
the basis of a careful evaluation of all relevant
factors and in consultation with the agencies
responsible for the design and construction of the
reinforced soil structures.
17.3 Important aspects to be considered while
finalizing the key elements of the subsurface
investigation programme include:
a) The type of the reinforced soil structure and
performance requirements – reinforced soil
structures retaining embankments, hillside
fills or load bearing abutment; height and
face inclination of reinforced soil
structure, width of embankment; type of
reinforcement – geosynthetic/metallic;
b) Topography of the site;
c) Ground conditions — Selection of
appropriate field tests and sampling
methods require some information on the
nature of the strata anticipated. This
information may be available from desk
study, previous investigations in nearby
locations, investigations done during
feasibility and preliminary investigation
phases and local experience;
d) Poor ground conditions — Requirements
for investigations may be more stringent in
the case of poor ground conditions like
very soft and soft clays, organic soils, deep
deposits of weak and compressible soils
etc, for example, more number of boreholes
and soundings, deeper boreholes and
soundings; and
e) Seismicity — Liquefaction of the
foundation strata is an important
consideration in Seismic Zone IV and
Zone V.
17.4 The agency responsible for designing the
reinforced soil structures should be actively
involved in the technical aspects at all stages of the
subsurface investigation programme.
a) Finalization of the key elements of the
subsurface investigation program during
the planning phase;
b) Termination of boreholes, additional
boreholes, tests, any changes in the
programme, etc during the fieldwork
phase;
c) Finalization of the laboratory test
schedules; and
d) Review the factual and
interpretative geotechnical/geological/
geophysical investigation reports to
ensure that the reports include
necessary and sufficient information for
the design.
18 EXPLORATION METHODS
18.1 Trial Pits
Trial pits shall be excavated to the required depth to
collect samples and perform relevant tests. The four
sides of the pits if needed, shall be stabilized by
either telescoping (stepped excavation) or by
shoring and strutting. In every trial pit, including
those excavated for tests, pocket penetrometer tests
shall be generously carried out at different depths in
different strata in plastic soils.
The soil profile for all four walls of the trial pit shall
be logged. Each wall shall be identified with respect
to compass direction. Measurement of depths from
the ground surface to the boundaries of various strata
shall be measured at the four corners of the pit.
Disturbed Sample locations shall spread over the
marked area in the borrow area.
18.2 Standard Penetration Test (SPT)
Standard Penetration Tests shall be carried out in a
borehole as per IS 2131, generally at 3.0 m intervals
and at every noticeable change of stratum. The first
test shall generally begin at 1.0 m to 1.5 m depth,
unless UDS can be collected at that depth.
Generally, SPT and UDS shall be conducted
alternatively at 1.5 m intervals. If UDS cannot be
collected at a depth owing to subsoil conditions, it
shall be replaced by the SPT below the disturbed
zone during the sampling attempt. Samples from the
split spoon sampler of SPT shall be maintained as
disturbed samples.
SPT shall also be conducted in weathered/soft rock
with rock quality designation (RQD) less than
25 percent. Its procedure shall be the same as for soil
except that penetration for 20 and 100 blows shall be
noted.
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18.3 Vane Shear Test (VST)
Field vane shear tests shall be conducted in
boreholes with very soft to firm cohesive strata, as
per procedure in IS 2720 (Part 30), to evaluate shear
strengths, particularly where undisturbed samples
are difficult to collect.
At each test location, the vane shear test shall be
conducted in two stages;
a) In the first stage, the test shall be done in
undisturbed soil; and
b) In the second stage, the test shall be
conducted on the remoulded soil.
18.4 Permeability Test
Permeability tests shall be conducted following
IS 5529 (Part 1) for soils and rocks in a borehole, as
per the design and construction requirements.
The test shall be conducted as a series of tests at
different pressures at a given depth. A series of three
tests is desirable with the maximum pressure applied
in three equal increments, then reduced with
decrements of the same amount.
18.5 Static Cone Penetration Test
This test shall be conducted as per IS 4968 (Part 3).
An electric cone shall be preferred for testing over
the mechanical cone.
18.6 Geophysical Methods
Geophysical methods shall be used as per the
requirements of the project and the expected site
conditions. Depending on the requirements, one or
more of the following methods can be adopted:
a) Seismic Refraction — in normal soil
profile conditions;
b) Multichannel Analysis of Surface Waves
(MASW) — in both normal and irregular
soil profiles;
c) Cross Hole Seismic Tests — using three
boreholes, one for source and two for
receivers;
d) Electrical Resistivity Method — to
determine soil resistivity or detect weak
zones under hard strata; and
e) Ground Penetrating Radar — to detect
utilities and other anomalies in the
subsurface.
Geophysical investigations shall be treated as
supplementary testing and not a substitute for direct
physical testing in geotechnical investigations.
18.7 Calibration of Equipment for Testing
All the equipment/instruments for any of the above
methods shall be properly calibrated at the start of
the work to reflect factual values. The instruments
shall be tested at an approved laboratory, and the test
reports shall be made available.
19 NUMBER, LOCATION AND SPACING OF
BOREHOLES
19.1 Reinforced Soil Structures
The number, spacing and location of boreholes shall
be decided with a view to obtain reasonably reliable
and sufficiently detailed information on the
subsurface conditions along the alignment of the
reinforced soil structures. The recommendations
given in the Table 1 shall be considered as
minimum requirements.
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Table 1 Minimum Requirement for Number, Location and Spacing of Boreholes
(Clause 19.1)
Sl No. Type of Reinforced Soil
Structure
Height/Ground
Conditions
Number/Spacing/Location of
Boreholes
(1) (2) (3) (4)
i) Reinforced soil walls and steep
slopes on reasonably level
ground retaining embankments
Height 10 m or poor
ground conditions(1)
50 m(2)(3) (4) (5) (6) (7) (8)
ii) Height 10 m or other
than poor ground
conditions
100 m(2) (3) (4) (5) (6) (7) (8)
iii) Reinforced soil closure walls of
approach embankments
Minimum two boreholes(9)
iv) Reinforced soil true/load bearing
abutments
Minimum two boreholes (9)
v)
Reinforced soil shallow slopes
on reasonably level ground
retaining embankments
Height 10 m or poor
ground conditions(1)
100 m(2) (3) (4) (5) (6) (7) (8)
vi) Height 10 m or other
than poor ground
conditions
200 m(2) (3) (4) (5) (6) (7) (8)
vii) Hillside reinforced soil walls and
slopes
100 – 200 m(10)
viii) Basal reinforced embankments
on poor ground
100 m(2)(3) (4) 5) (7)
(1)
Poor ground conditions include a) Soils having low shear strength and high compressibility like very soft/soft/medium stiff clays
and silts (SPT N 8 or undrained shear strength 50 kPa) and organic soils, b) Very loose/loose sands (SPT 10)
susceptible to liquefaction.
(2)
In the case of embankments, the recommended spacing is for the embankment as a whole. The boreholes should be distributed on
both sides of the embankment to evenly cover the reinforced soil structures on either side.
(3)
At least one borehole should be at the location of the maximum height of reinforced soil structure/embankment.
(4)
At critical locations (for example, location of maximum height of reinforced soil structure/embankment), one to two additional
boreholes or SCPT may be carried out outside the footprint of the reinforced soil structure/embankment to assess the
subsurface conditions in a direction perpendicular to the alignment of the reinforced soil structure/embankment for global
stability analysis.
(5)
Where subsurface conditions are favourable up to 30 percent of the boreholes may be replaced by static cone penetration tests
(SCPT), subject to the approval of the engineer.
(6)
At locations where rock/weathered rock is encountered at a shallow depth, which can safely support the reinforced soil structure,
test pits may be used instead of boreholes, subject to the approval of the engineer.
(7)
For reinforced soil structures and embankments with a length of more than 500 m, it is recommended to carry out geophysical
investigations. Where geophysical investigations are carried out complying with the requirements of this code, the spacing of
boreholes may be increased up to twice the value prescribed above.
(8)
Boreholes shall be located within or very close to the footprint of the reinforced soil zone as far as possible, except for (4)
as noted
above.
(9)
Boreholes shall be located within the footprint of the reinforced soil zone, preferably one borehole each close to the ends of the
reinforced soil wall.
(10)
For reinforced soil walls and slopes in hilly areas, access to drilling equipment may be a significant constraint. In such cases, it is
advisable to use a judicious combination of geophysical methods and boreholes, which may be finalized in consultation with an
engineering geologist during the planning phase. The engineering geologist is expected to reconnaissance the site, map geological
features, and identify suitable locations for investigations.
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19.2 Borrow Areas and Ash Ponds
The geotechnical testing shall be carried out for
1 sample per 3 000 m3
of soil from the prospective
borrow area. Hence, the location and spacing of
geotechnical test points shall depend upon the
estimated areal extent of the borrow area and/or ash
pond.
Geotechnical investigations shall be carried out by
trial pits, which may be followed by boreholes for
deeper exploration, as per need.
20 DEPTH OF EXPLORATION
20.1 Geophysical Tests
Depth of exploration by geophysical investigations
is generally guided by the purpose of the
investigation and the geometry of reinforced soil
structure:
a) For detecting utilities, the depth of
exploration can be up to 5 m;
b) For other anomalies in soil strata, it shall be
at least 10 m or 1.5 times the height of
structures whichever is higher; and
c) For seismic design, if needed, the depth of
explorations shall be at least 30 m.
20.2 Trial Pits
Owing to inherent limitations, the depth of
exploration with trial pits is limited to 6 m or within
weak or weathered rock. Trial pits are generally
clubbed with boreholes that do not have major
limitations for depth of exploration.
20.3 Borehole Investigations
20.3.1 The depth of borehole exploration shall be
sufficient to investigate all strata which may
experience a significant increase in stresses due to
the loads imposed by the reinforced soil structures
and retained fills and which may undergo shear
failure, significant deformation, or liquefaction,
thereby influencing the stability or serviceability of
the reinforced soil structures.
20.3.2 The depth of investigation should be decided
based on the zone of interest or significant influence
for different design limit states. The depth of the
zone of interest for different design limit states is as
follows:
a) Bearing capacity of reinforced soil
structure: 1.5 times the height of the
reinforced soil structure;
b) Overall bearing capacity of embankment:
Width of embankment;
c) Settlement: 4 times the width of
embankment/hill-side fill; and
d) Liquefaction: 25 m.
20.3.3 The depth of boreholes/soundings shall be
sufficient to obtain the required information for all
weak/compressible/liquefiable strata within the
zone of interest.
20.3.4 As a general rule, the depth of
boreholes/soundings shall not be less than the
values recommended in Table 2.
20.4 Static Cone Penetration Tests
Owing to practical limitations of the static cone
apparatus, the maximum depth of exploration does
not generally exceed 10 m to 15 m, depending on the
subsurface strata encountered.
21 SELECTION OF TYPE OF TEST
The field and laboratory test methods for each type
of strata should be chosen appropriately to
determine geotechnical design parameters. General
guidance is given in the Table 3.
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Table 2 Recommendations for Minimum Depth of Boreholes
(Clause 20.3.4)
Sl No. Type of Reinforced Soil Structures Minimum Depth of Boreholes/Soundings
(1) (2) (3)
i) Reinforced soil walls and slopes
retaining embankments, closure walls
of approach embankments; true
abutments
Least of the following: (1) (2) (3)
a) Four times the height of the
reinforced soil structure
b) Two times the average width of
embankment
c) 30 m
ii) Hillside reinforced soil walls and
slopes
Least of the following: (1) (3)
a) Four times the height of the
reinforced soil structure
b) 30 m
iii) Basal reinforced embankments Least of the following: (1) (2) (3)
a) Two times the average width of
embankment
b) 30 m
(1)
Boreholes may be terminated if the rock or weathered rock with SPT N  100 is encountered at a depth  10 m;
in such cases drilling into rock is not usually required. When rock is encountered at a depth less than 10 m, the
continuity of rock strata must be ensured by drilling a minimum of 3 m into the rock.
(2)
At locations with deep deposits of compressible soils, boreholes/soundings shall extend to all layers of organic
soils and fine-grained soils (clays/silts) with a consistency ranging from very soft to stiff (SPT N 15 or
undrained shear strength 100 kPa), within the zone of interest. Caution must be exercised at sites where silt/clay
strata alternate with sand/gravel strata. At such locations, the depth of exploration should be decided based on
the understanding of local geology and past experience.
(3)
In seismic zone IV and zone V minimum depth of boreholes and soundings shall not be less than 25 m unless the
rock is encountered at a lesser depth.
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Table 3 Selection of Type of Tests Based on Subsoil Strata
(Clause 21)
Sl No. Design Limit
State
Property Type of Soil Suitable Remarks
Preferred Acceptable
(1) (2) (3) (4) (5) (6) (7)
i) Bearing capacity/
global stability
Effective angle
of shearing
resistance ()
Sands SCPT, SPT, PMT, DMT 1) Laboratory tests on
reconstituted samples may not
correctly represent in-situ
conditions.
2) For PMT, borehole diameter
should be uniform and
compatible with the pressure
meter and borehole sides shall
be stable.
Gravels SPT, PMT
Residual soils SPT, PMT
Undrained shear
strength (su)
Very soft/soft
clays/silts
FVST SCPT SPT may be used with caution
when it is not practically
feasible to conduct FVST or
CPT.
Medium stiff to
stiff clays/silts
SCPT, PMT,
Lab tests on
good quality
UDS
SPT Driving the sampler using
impact shall be avoided.
Very stiff to hard
clays/silts PMT, SPT, SCPT
Use of SCPT is limited to its
reaction capacity.
ii) Settlement
Drained modulus
(E)
Sands SCPT, PMT,
DMT
SPT
Gravels PMT, SPT
Residual soils PMT, SPT
Undrained
modulus (Eu)
Clays/silts SCPT, PMT,
DMT
SPT
e0, Cc, Cr, p, cv Clays/silts Consolidation tests on good
quality UDS
Correlations with liquid limit,
water content etc are not
reliable
iii) Liquefaction Sands SPT, SCPT, Vs
where
SCPT = Static cone penetration test;
SPT = Standard penetration test;
PMT = Pressure meter test;
FVST = Field vane shear test;
DMT = Dilatometer test;
UDS = Undisturbed sample;
Vs = Shear wave velocity;
e0 = Initial void ratio;
Cc = Compression index;
Cr = Recompression index;
p = Pre-consolidation pressure; and
Cv = Coefficient consolidation in vertical direction.
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22 BORING AND SAMPLING
22.1 Boring in Soils
a) Hand-held augers can be used to drill for
shallow depth, generally restricted to site
reconnaissance activities; and
b) Mechanised boring shall be used to create
deep boreholes. Three primary methods of
mechanised boring are:
1) Percussion drilling w/o casing;
2) Wash boring; and
3) Rotary drilling.
During boring, unnecessary disturbance to the soil
should be avoided, particularly through non-plastic
and dry soils, soft to medium stiff clay strata. The
net hydraulic head at the bottom of the borehole is
zero or slightly on the positive side within the
borehole. Close-fitting tools such as bailer shall be
withdrawn slowly to avoid suction pressures:
a) Diameter of Boreholes — It shall permit
collecting undisturbed samples of 90 mm
to 100 mm diameter. Typically, the
borehole diameter is about 150 mm; and
b) Casing in Boreholes — If a borehole
requires casing, the casing bottom shall be
maintained within 150 mm from the
borehole bottom unless it reaches a stratum
requiring no casing. The casing shall never
be in advance of the borehole bottom
during undisturbed sampling, standard
penetration tests, and other in-situ tests.
22.2 Drilling in Rock
a) Boring in rock strata shall be done by using
a rotary cutting tool tipped with tungsten
carbide bits, though diamonds bits are
preferred for better core recovery;
b) Drill-hole size shall generally be
NX (76 mm);
c) Core barrels shall normally be double-tube
ball-bearing, swivel type, with the core
lifter (catcher) located in the lower end of
the inner barrel. A triple-tube core barrel
shall be used where the rock is highly
fragmented and the rock quality
designation (RQD) is less than 10 percent;
d) Drilling shall be carried out in such a
manner that maximum core is recovered;
e) Coring runs shall be limited to a maximum
length of 3.0 m. When less than 50 percent
core length is recovered from a run or when
a geological feature is to be accurately
determined, the length of the run can be
reduced up to 0.3 m unless directed
otherwise by the geotechnical engineer;
f) The core shall be removed from the
drill-hole immediately if blocking of the bit
or grinding of the core is apparent,
regardless of the length of the run made
thus far;
g) The ease or difficulty of drilling at different
depths shall be carefully noted and
recorded during drilling. The returning drill
water shall be kept constantly under
observation, and its character, such as
clarity, turbidity, colour, shall be recorded;
h) Core recovery and rock quality designation
(RQD) shall be noted for each run
immediately after cores are taken out of the
barrel; and
j) Each core piece shall be serially and
sequentially numbered from the top
downwards as soon as the core pieces are
removed from the core barrel and
accordingly placed in core boxes.
22.3 Soil Sampling
22.3.1 Undisturbed Soil Sampling in Boreholes
22.3.1.1 Undisturbed soil samples (UDS) shall be
generally collected at every 3.0 m interval and at
every identifiable change of soil formation. Samples
shall be minimum 90 mm diameter and generally
450 mm long, as per IS 2132.
22.3.1.2 Thin-walled open drive sampler, as per
IS 2132, shall be generally used for sampling. Its
tube and cutting shoe (or edge) shall be free from
rust, pitting, burring, or other defects. Use of oil
inside the sampler shall be at the minimum
practicable.
22.3.1.3 The collection of undisturbed samples in
non-cohesive (sand and silty soil) strata is difficult.
Piston samplers, mazier samplers or other
specialised sand samplers shall be used, but with
utmost precautions.
22.3.1.4 The borehole bottom shall be cleaned
carefully before sampling. Every care shall be taken
to avoid disturbance of material to be sampled. The
sampler shall be lowered to the borehole bottom
without impact and pressed into the soil in a single
continuous movement at a slow rate. The sampler
shall never be pushed or driven to its full length to
avoid any pressure on the sample collected inside the
sampler.
22.3.2 Disturbed Soil Samples
22.3.2.1 Disturbed soil samples shall be taken at
every 1.5 m interval and at every significant change
of stratum in a borehole. The samples shall be placed
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without delay in air-tight glass jars or sealed
polythene bags.
22.3.2.2 Bulk disturbed samples from boreholes or
trial pits shall be collected if the material in the
ground includes gravel or cobble-sized particles.
Such samples shall be representative. Unless
specified, it shall be a minimum of 3 kg when
collected from boreholes and 10 kg when collected
from trial pits. The samples shall be sealed into
heavy-duty polythene bags immediately after they
are collected.
22.4 Water or Leachate Samples
22.4.1 Water samples shall be collected from
boreholes and at the trial pits, as specified. Likewise,
leachate samples shall be collected from areas
storing pond ash if it is to be used as reinforced fill
or backfill.
22.4.2 The water/leachate sample shall be collected
in an airtight, scrupulously clean glass, inert HDPE
bottle, or jerry can. The bottle or can should be
rinsed three times with water/leachate being
sampled before filling with the sample. The quantity
of each sample collected shall be about 1 litre.
22.4.3 The water/leachate samples shall be tested as
soon as possible after sampling, for sulphate (SO3)
and chloride contents and its pH, and for other
cations and anions as required, with due
consideration to the material of geosynthetics
proposed for the system.
22.5 Sealing and Labelling Samples
22.5.1 Immediately after taking an undisturbed
sample in a tube, the cutting shoe and the adapter
head shall be removed along with the disturbed
material in that. The visible ends of the sample shall
each be trimmed off any wet disturbed soil. The ends
shall then be coated alternately with four layers of
just molten microcrystalline wax or other similar
material. Any space remaining at the ends of the
sample tube shall be solidly filled with damp saw
dust or other similar material. The ends of the
sample tube shall be covered with tight-fitting caps,
preferably screw caps.
22.5.2 Block samples collected from trial pits
shall be coated with a succession of layers of
microcrystalline wax, preferably reinforced with
layers of needle punched nonwoven. These samples
should be packed in a suitable material and placed in
a strong case. Large samples shall be provided with
a tight-fitting formwork or packed in a rigid cement
or resin to prevent fissure opening under their
self-weight.
22.5.3 All samples shall be clearly labelled,
indicating job number, borehole number, sample
number, date of sampling, a brief description of the
sample (type, elevation etc). The top or bottom of
undisturbed samples shall be clearly labelled. Each
such label shall be pasted on the container and
another shall also be placed inside the container.
22.6 Transporting and Storing Samples
22.6.1 Sampling tubes containing undisturbed soil
samples shall not be exposed to direct sun and shall
be kept in shade covered with wet nonwoven
material. These tubes shall be transported in robust
containers with the packing of polyurethane foam or
other similar resilient material.
22.6.2 Rock cores shall be segregated accurately for
each run by labelled separator blocks of at least
25 mm thickness. No box shall contain more than
6 m of the core. Depths of all runs shall be marked
on the partitions with indelible paint. The core boxes
shall be prominently marked “FRAGILE, HANDLE
WITH CARE” and the TOP and BOTTOM of the
box shall be clearly marked.
22.6.3 Shipping of the samples to the testing
laboratory and their testing shall be completed as
early as possible. All unused and excess samples,
after testing, shall be retained and properly stored for
three months after the report submission.
22.7 Specific Observations During Boring
The following observations shall be noted during
boring:
a) Sequence and thickness of different strata;
b) Visual description and thickness of each
stratum, including soil type, consistency,
colour etc;
c) Groundwater table;
d) Joints, fissures, artesian conditions etc;
e) Spacing, condition and orientation of
discontinuities;
f) Rock quality designation (RQD); and
g) Presence of lime, mica etc.
22.8 Backfilling of Boreholes
The boreholes must be appropriately backfilled
immediately after the boring is completed.
23 LABORATORY TESTS
23.1 Soil and water/leachate samples procured
during geotechnical fieldwork shall be tested/
analysed in an appropriate laboratory. All laboratory
tests shall be performed by qualified and
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experienced personnel familiar with and having
access to equipment and facilities to accurately
determine data necessary for requirements under this
code.
23.2 Laboratory tests shall be carried out in
accordance with the prescribed procedures in the
relevant BIS codes of practice, standards and
guidelines and/or other specific requirements
indicated for the project. In case of any anomalies or
contradictions between field observations and
laboratory test results, the laboratory tests shall be
repeated as long as the sample is available.
23.3 Laboratory tests on foundation/subgrade
material shall be according to tests routinely
conducted on foundations of structures. Tests shall
include the requirements to determine expansive
characteristics of the overburden as well as the
potential for liquefaction of subsurface soil strata in
Seismic Zone III upwards.
23.4 The disturbed soil samples from borrow areas
shall be tested at least for the following:
a) Grain size distribution, including
determination of fines (less than
75 microns) and clay content (less than
2 microns);
b) Liquid limit, plasticity index, shrinkage
limit on fines fraction, if any;
c) Compacted dry density — Moisture
content relationship by the modified
proctor method and determination of
maximum dry density and optimum
moisture content. Filter materials should be
self-compacting, its dry density shall be
measured by light hand tamping;
d) Free swell index test on a representative
soil sample. Soil with more than 25 percent
swell index shall not be used as any of the
fill;
e) Permeability test on samples compacted to
95 percent modified proctor density. Filter
material should also be tested at light hand
tamping density;
f) Consolidated drained test or direct shear
tests, as applicable, on samples at optimum
moisture content condition, compacted to
95 percent modified proctor density; and
g) Chemical analyses of the material
including its pH, sulphates and chloride
contents, particularly if pond ash is the
backfill material.
23.5 Water and leachate samples shall be routinely
tested for pH and sulphate and chloride contents.
Leachates from pond ash shall particularly be tested
for ions that can be detrimental in any manner to the
material of geosynthetics (uncoated and
unprotected) being used, even if the geosynthetic
reinforcement is adequately coated. While normal
reduction factors for environmental deterioration
may be considered, it is necessary to study reduction
factors for the geosynthetic, considering the ions and
their concentrations detected in the leachate.
24 THE REPORT
24.1 Essence of the Subsurface Investigation
Report
24.1.1 The report shall generally contain the
geological history of the site, and field and
laboratory observations and test results. It shall
include details of boreholes and pits, geophysical
sections, summarised test data, observations and
conclusions. It shall essentially be in SI units.
24.1.2 Actual/raw field data and laboratory
observations, and calculations of test results shall be
made available along with the report.
24.1.3 The observations and results shall, in general,
be summarised as per the format given in Annex D.
However, it can be modified as per the findings and
project requirements.
24.2 Contents of the Report
The report shall at least include the following, as
applicable:
a) Plot plan with marked locations of all
sampling and test locations;
b) Layout of the borrow area or ash pond with
marked locations of trial pits, boreholes,
and leachate samples, as applicable;
c) Generalised subsurface profiles along
various sections along with the SPT values
and other sounding test results;
d) Geophysical test interpretations for
subsurface profile and observations of the
water table and any peculiar conditions
such as artesian conditions, sand blow;
e) Graphical representation of cone
penetration test results including tip
resistance and friction;
f) Rock mass rating as per the field
observations and IS 13365 (Part 1);
g) Chemical analyses results of groundwater
and leachate samples along with details of
locations and depths of sampling; and
h) Summary of testing results, field as well as
the laboratory, including relevant graphs,
charts diagrams.
A typical format for summarising the borehole and
test pit results is given in Annex D.
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SECTION 3 MATERIALS
25 SCOPE
This section specifies the requirements of different
materials to be used in reinforced soil structures. All
the designs and construction should conform to the
specifications detailed in this chapter.
26 FILL MATERIAL
26.1 In reinforced soil (RS) structures,
geosynthetics/metallic reinforcement, fill material,
drainage arrangement and facing elements are the
major components. Unlike reinforced concrete
cantilever retaining wall, soil fill, and
geosynthetics/metallic reinforcement with facings
form a reinforced mass and act together as a
retaining structure. The engineering properties of a
reinforced fill and retained fill material in reinforced
soil structures are of critical importance thus should
be given special consideration. The reinforced fill
material should be a select fill and must conform to
the properties as specified. Fig. 1 gives a schematic
diagram showing different fills in reinforced soil
structure.
26.2 The selection criteria of reinforced fill should
consider the completed structure's long-term
performance, construction phase stability, and the
degradation environment created around the
reinforcements. Much of engineering communities’
knowledge and experience with reinforced soil walls
(RSW) structures to date has been with select,
cohesionless backfill. Granular soils are ideally
suited to reinforced soil walls (RSW) and reinforced
soil slope (RSS) structures. The conservative
reinforced fill property criteria cannot completely
replace a reasonable degree of construction control
and inspection.
26.3 In general, these select reinforced fill materials
could be more expensive than lower-quality
materials. The specification criteria for each
application (walls and slopes) differ somewhat
primarily based on the completed structure's
performance requirements (allowable deformations)
and the design approach. The following sections
provide the fill requirements.
26.3.1 Granular Fill : Select Material for the
Reinforced Zone of Walls
26.3.1.1 Reinforced soil walls require high-quality
fill for durability, good drainage, constructability,
and good soil reinforcement interaction which can
be obtained from well-graded, granular materials.
The performance of the reinforced soil wall mainly
depends on the friction between reinforcement and
soil. Hence, a fill material with high frictional
characteristics is required and generally specified in
practice. The performance requirements generally
eliminate soils with clay contents. From a
reinforcement capacity point of view, lower quality
wall fills could be used for RS wall structures;
however, a high quality granular wall fill has the
advantages of better drainage, providing better
durability for metallic reinforcement, and requiring
less reinforcement. There is also significant
handling, placement and compaction advantages in
using granular soils. These include an increased rate
of wall erection and improved maintenance of wall
alignment tolerances.
26.3.1.2 In general, all fill material used in the
structure for RSW structures should be free from
organic or other deleterious materials. It should
conform to the gradation limits, plasticity index (PI)
and soundness criteria listed below, and this presents
a broad gradation range that is applicable across the
country. Unstable broadly graded soils and gap
graded soils should be avoided. These soils tend to
pipe and erode internally, creating problems both
with loss of materials and clogging the internal
drainage systems. Table 4 gives the requirements of
a select reinforced fill for an RS wall.
26.3.1.3 While using metallic reinforcement or
metallic connection system, it should be ensured that
the fill's electro-chemical properties are satisfactory
and would not cause or trigger corrosion of the
reinforcement. The soil shall have a resistivity of
more than 5 000 ohm-cm at saturation. The water
extract from the soil should not have chlorides more
than 100 ppm, sulphates do not exceed 200 ppm
and pH ranges from 5 to 10. Metallic reinforcement
should not be used for soils with a resistivity of less
than 1 000 ohm-cm.
26.3.1.4 Water used for compaction shall have a
resistivity of more than 700 ohm cm. Besides, the
water used for compaction shall have sulphates as
SO3 less than 400 mg/lit, chlorides less than
2 000 mg/l, and pH not less than 6, organic content
less than 200 mg/l and suspended matter less than
2 000 mg/l. All the above chemical tests should be
done as per IS 3025.
26.3.1.5 The compaction specifications should
include a specified lift thickness and the allowable
range of moisture content with reference to the
optimum. Compaction moisture control should be
± 2 percent of optimum moisture content and
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compaction should be based on 95 percent of
maximum dry density [Heavy compaction
IS 2720 (Part 8)], compaction methodology of
reinforced fill are different near the wall facing
within 1.5 m. Lighter compaction equipment
(for example: walk-behind vibratory plate or roller)
and thinner lifts (maximum compacted layer
thickness is the same as the fill compaction layer
thickness) should be adopted near the wall face to
prevent the build-up of high lateral pressures and
facing panel movement.
FIG. 1 SCHEMATIC SHOWING DIFFERENT FILLS IN A REINFORCED SOIL STRUCTURE (NOT TO SCALE)
Table 4 Select Granular Fill Requirements for Reinforced Soil Walls
(Clauses 26.3.1.2 and 26.3.5)
Sl No. IS Sieve Size Percent Passing
(1) (2) (3)
i) 75 mm 100
ii) 425 micron 60 to 90
iii) 75 micron 0 to 15
NOTES
1 The plasticity index IS 2720 (Part 5) should be less than or equal to 6 and Cu should be greater than 2.
2 Fill containing soil greater than 15 percent passing 75 micron sieve, but less than 10 percent of particles smaller than
15 microns are acceptable. The plasticity index should be less than 6 and the drained angle of internal friction should
not be less than 30°.
3 By keeping in mind about the construction survivability of geosynthetics and epoxy coated reinforcements, it is
recommended that the maximum particle size for these materials be reduced to 19 mm for geosynthetics and epoxy and
PVC coated steel reinforcements unless construction damage assessment tests are or have been performed on the
reinforcement combination with the specific or similarly graded large size granular fill.
4 The materials shall be substantially free of shale or other soft, poor durability particles. The material shall have a
magnesium sulphate soundness loss of less than 30 percent after four cycles or a sodium sulphate value less than
15 percent after five cycles [soundness test as per IS 2386 (Part 5)].
IS 18591 : 2024
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Method of
Test, Ref. to
IS 2720
(Part 4)
(4)
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26.3.2 Select Reinforced Fill for Reinforced Soil
Slopes
26.3.2.1 RSS structures are normally not constructed
with rigid facing elements. Less select reinforced fill
can be used for RSS since facings are typically
flexible and can tolerate some distortion during
construction. Even so, a high-quality embankment
fill meeting the following gradation requirements to
facilitate compaction and minimize reinforcement
requirements is recommended. Table 5 presents the
recommended reinforced fill requirements for
RSS construction.
26.3.2.2 RSS reinforced fill compaction should be
based on 95 percent of MDD [IS 2720 (Part 8)] and
± 2 percent of optimum moisture. Issues with
drainage problems, excessive distortion and
settlement must be carefully evaluated with
fine-grained and/more plastic soils.
26.3.3 Design Strength of Reinforced Fill
Materials
The angle of internal friction should not be less than
30° (see IS 2720 (Part 11) or IS 2720 (Part 12) or
IS 2720 (Part 13). In all cases, the cohesion of the
reinforced fill is to be neglected.
26.3.4 Retained Backfill and Natural Retained
Soil
26.3.4.1 Retained backfill can be different from the
reinforced fill. As with reinforced fill, a cohesion
value of zero is conservatively recommended for
the retained fill's long-term, effective strength. The
angle of internal friction should be greater than 25°
[see IS 2720 (Part 11) or IS 2720 (Part 12) or
IS 2720 (Part 13)] and PI should be less than
20 [IS 2720 (Part 5)] for the retained fill. The fines
content passing through 75 micron sieve shall be less
than 50 percent. Drainage detailing should be taken
care as per Section 9.
26.3.4.2 For back to back walls wherein the free
ends of the two walls' reinforcement are spaced apart
less than or equal to one-half the design height of the
taller wall, same material as reinforced fill should be
used for the space between the free ends of the
reinforcements as well.
26.3.4.3 If undisturbed samples cannot be obtained
for back cut construction, friction angles may be
obtained from in-situ tests or by correlations with
index properties. The strength properties are
required for the determination of the coefficients of
earth pressure used in design as well as for overall
stability analysis. In addition, the position of
groundwater levels above the proposed base of
construction must be determined in order to evaluate
hydrostatic stresses in the retained fill and plan an
appropriate drainage scheme to control groundwater
conditions. An appropriate drainage scheme behind
the reinforced zone also needs to design for the
reinforced wall to retain any waste materials and
poorly draining materials (refer Section 9).
Table 5 Fill Requirements for a Reinforced Soil Slopes
(Clauses 26.3.2.1, 26.3.5 and 42.2.1)
IS Sieve Size, µ Percent Passing
80 000 100
4 750 20 to 100
425 0 to 60
75 0 to 50
NOTES
1 The plasticity index of soil IS 2720 (Part 5) should be less than or equal to 20.
2 By keeping in mind about the construction survivability of geosynthetics and epoxy coated reinforcements, it is recommended
that the maximum particle size for these materials be reduced to 19 mm for geosynthetics and epoxy and PVC coated steel
reinforcements unless construction damage assessment tests are or have been performed on the reinforcement combination with
the specific or similarly graded large size granular fill.
3 Magnesium sulphate soundness loss has to be of less than 30 percent after four cycles (or a sodium sulphate value less than
15 percent after five cycles).
Sl No.
i)
ii)
iii)
iv)
(1) (2) (3)
IS 18591 : 2024
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Method of Test,
Ref. to
IS 2720
(Part 4)
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26.3.5 Pond Ash
In view of the abundant availability of pond ash in
India, it has been successfully utilised as a
backfill/reinforced fill in many inter changes
approaches. Pond ash is also generally preferred
material for RSS construction over weak
subsoil, both drained and undrained conditions.
IS 3812 (Part 2) provides description about pond ash
and bottom ash. Either pond ash or bottom ash can
be used as reinforced fill or retained fill. Chemical
requirements of pond ash and bottom ash for
reinforced fill or retained fill application shall be as
per Table 1 in IS 3812 (Part 2). The material shall
satisfy soundness test as per Table 2 of IS 3812
(Part 2).
Pond ash used for reinforced fill and retained fill
shall be free-draining and shall have PI 6 and
Cu 2. It is recommended to use pond ash with
MDD greater than 10 kN/m3
[IS 2720 (Part 8)]. The
minimum angle of friction of pond ash shall be 30°
[IS 2720 (Part 11) or IS 2720 (Part 12) or
IS 2720 (Part 13)]. Even if the pond ash material
does not meet the gradation criteria for backfill/
reinforced material (Table 4 and Table 5), this
criterion is relaxed, considering high shear strength
and good permeability characteristics of pond ash
or bottom ash.
Under no circumstances, multiple fill materials
should be used for a given stretch of wall/slope.
Metallic reinforcement should not be used in the
pond ash with a resistivity of less than 3 000 ohm
cm. The pond ash should not show chlorides more
than 100 ppm, sulphates do not exceed 200 ppm
and pH ranges from 5 to 10 when metallic
reinforcement is used.
During the construction, every care should be taken
for proper drainage of the reinforced fill portion, and
it shall be ensured that there is no movement of
particles of pond ash through the joints in the facing
panel. Further details can be referred in drainage and
construction Section 9 and Section 10.
26.3.6 Requirements for Natural Drainage
Materials
Typically, RS structures are not designed to
withstand hydrostatic pressures. Where hydrostatic
pressures are likely due to submergence, the design
should account for such pressure. To ensure that
these conditions are realised in the field, adequate
drainage measures need to be taken. A drainage bay
of a minimum 600 mm width at the back of the
facing is recommended. The desirable gradation of
the aggregate to be used in the bay is included in
Table 6. Besides meeting gradation requirements, it
should be ensured that the aggregates are not friable,
flaky, elongated and are sound in strength.
Alternatively, a geo-composite that ensures
adequate drainage can be provided. The typical
drainage detailing for RS structures under different
conditions is given in Section 9.
Table 6 Gradation Requirements for Drainage
Bay
(Clause 26.3.6)
Sl No. Sieve Opening Size
mm
Percentage
Finer
(1) (2) (3)
i) 37.5 90 to 100
ii) 20.0 80 to 100
iii) 12.5 0 to 20*
27 REINFORCEMENT MATERIALS
Reinforcements can be made from metals
(generally steel) or polymeric materials.
Reinforcement shall only be used if its suitability,
including durability, has been proven by trials or
experience, and by approved tests, carried out on the
product.
27.1 Steel Reinforcement
27.1.1 Hot Dip Galvanised Steel Strips
27.1.1.1 The steel strips shall be galvanized hot
rolled steel strip with transverse ridges to have high
pullout capacity type high adherence (HA) or thicker
at connection point type high adherence reinforced
(HAR) strips.
27.1.1.2 The steel strips shall have minimum tensile
strength of 490 MPa complying with the
requirements of IS 2062 with minimum elongation
(on base metal) of 18 percent or the steel strips shall
have minimum tensile strength of 550 MPa and yield
strength of 450 MPa complying with minimum
guaranteed elongation (on base metal) of 17 percent.
The steel strip shall have minimum tensile, bearing
and shear strength of 490 MPa, complying with the
requirement of IS 2062. Fig. 2 shows typical steel
strip reinforcement used in reinforced soil walls and
Fig. 3 shows the typical connection details.
27.1.1.3 The steel strips shall be positively
connected using nuts and bolt with the facing panels
by using lugs, which are placed during pre-casting.
The panel lugs are manufactured from hot-rolled
steel strip. The steel strip used for lugs should have
minimum tensile of 490 MPa, complying with the
*The fines (passing 0.075 mm sieve) preferably be 0 percent to 5 percent.
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requirement of IS 2062, except the elongation
(on base metal) shall be minimum 22. After
fabrication, the HA and HAR strips and panel lugs
are hot dip galvanized requirements as per IS 4759,
except that the average zinc coating weight is not
less than 520 g/m2
(75 micron).
27.1.1.4 Reinforcing strips shall be cut to the lengths
and tolerances shown on approved drawings. Holes
for bolts shall be punched in the locations shown.
They shall be carefully inspected to ensure they are
true to size and free from defects that may impair
their strength or durability. The chemical
requirement of the steel listed below as soil
reinforcement shall be as given in Table 7.
Nominal dimensions and the design strength of the
strips and panel lugs for 100 years of design life are
given in Table 8.
Table 7 Chemical Requirement of the Steel Reinforcement
(Clause 27.1.1.4)
Table 8 Minimum Dimensions of Steel Strips and Panel Lugs
(Clause 27.1.1.4)
Sl No. Characteristics Requirement, Percent
Max
(1) (2) (3)
i) Carbon: C 0.24
ii) Manganese: Mn 1.6
iii) Phosphorus: P 0.045
iv) Sulphur: S 0.045
v) Silicon: Si 0.55
Sl No. Material
Requirements
Type Nominal
Width
(mm)
Nominal
Thickness
(mm)
Design Strength (1)
, TD (kN)
(1) (2) (3) (4)
Main Body Connection
(6) (7)
i)
As per IS 2062
40 5 40.87 30.42
ii) 40 4 – 39.02
iii) 45 5 44.9 44.9(2)
iv)
405 Ribbed strip
405 Ribbed lug
455 Ribbed strip
455 Ribbed lug 45 4 – 47.56
(1)
Assumes a design life of 100 years.
(2)
Connection capacity limited by main body strength.
(5)
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FIG. 2 SCHEMATIC OF TYPICAL CARBON STEEL STRIP
FIG. 3 SCHEMATIC OF CONNECTION WITH STEEL STRIP
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27.1.2 Fasteners
Bolts and nuts shall be hexagonal in shape and high
strength screw conforming to IS 1364 (Part 3). They
shall be 12 mm in diameter 40 mm in length with
shank, hot-dip galvanized conforming to IS 5358.
27.1.3 Ladder Soil Reinforcement
The ladder reinforcement shall be made of steel bar
of minimum 8 mm diameter of grade Fe 500 or
Fe 415. The cross welded bars shall be minimum
8 mm diameter of 150 mm centre to centre spacing
of same grade. The welding shall be done by electric
fusion welding process at factory. The ladder soil
reinforcement shall be galvanized as per IS 2629
except the zinc coating which shall be minimum
520 g/m2
.
27.1.4 Hot-Dip Galvanized Prefabricated Welded
Steel Mesh
The galvanized welded steel mesh shall be made
from hard drawn steel wire having minimum
diameter of 8 mm and complying with IS 432
(Part 2), galvanization shall be done as per IS 2629
except the zinc coating which shall be minimum
610 g/m2
. The welding shall be done by electric
fusion welding process at factory.
27.2 Polymeric Reinforcement
27.2.1 Polymeric reinforcement can take many
forms, such as strips, grids or sheets. Like steel
strips, polymeric strips shall be installed at
predetermined vertical and horizontal spacing
required by design. In contrast, only vertical spacing
shall be specified for grids or sheets installed as
full-width (or with coverage ratio) reinforcement.
27.2.2 As required by the design, polymeric
reinforcement shall be provided with certified values
of design strengths pertaining to the specified design
life and operating temperature of the reinforced fill
structure and, based on tensile creep rupture and
isochronous load-strain characteristics. The geogrid
and geostrap used as polymeric reinforcement
materials in walls and slopes shall conform to the
IS 17373 and IS 17372 respectively. The woven
geotextile made from virgin polymer of polyester and
polypropylene used for walls and slopes shall
conform to the requirements specified in Table 9 and
Table 10 respectively. The woven geotextile made
from virgin polymer of polyester used for basal
reinforcement shall conform to the requirements
specified in Table 11. The geogrid used for basal
reinforcement shall conform to requirements specified
in IS 17373.
(Clause 27.2.2)
Sl No. Characteristics Requirements Method of Test,
Ref to
(1) (2) (3) (4)
i) Ultimate tensile strength (machine
direction: MD), kN/m
≥ 60 IS 16635
ii) Ultimate tensile strength (cross
direction: CD), kN/m
≥ 20 IS 16635
iii) Elongation at ultimate strength
(MDCD), percent
≤ 15 IS 16635
iv) Chemical resistance, strength retained
after 72 h immersion, percent
≥ 70 IS 17363
NOTES
1 Molecular weight of the polyester polymer shall be greater than 25 000 g/mol.
2 Carboxyl end groups 30 mmol/kg.
3 The design strength of reinforcement shall be calculated as per method given in Section 4.
Table 9 Requirements of Woven Geotextile Made from Virgin Polymer of
Polyester for Walls and Slopes
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Table 10 Requirements of Woven Geotextile Made from Virgin Polymer of Polypropylene
for Walls and Slopes
(Clauses 27.2.2 and 42.4)
Sl No. Requirement Method of Test, Ref to
(1)
Characteristics
(2) (3) (4)
direction: MD), kN/m
≥ 60 IS 16635
ii) Ultimate tensile strength (cross direction:
CD), kN/m
≥ 20 IS 16635
iii) Elongation at ultimate strength in MD and
CD, percent
≤ 35 IS 16635
iv) Chemical resistance, strength retained after
72 h immersion, percent
≥ 70 IS 17363
NOTE — The design strength of reinforcement should be calculated as per the method given in Section 4.
Table 11 Requirements of Woven Geotextile Made from Virgin Polymer of Polyester — Basal
Reinforcement
Sl No. Characteristics Requirement Test Method,
Ref to
(1) (2) (3) (4)
direction: MD)
≥ 100 kN/m IS 16635
ii) Ultimate tensile strength (cross
direction: CD)
≥ 20 kN/m IS 16635
iii) Elongation at ultimate strength
(MDCD)
≤ 15 % IS 16635
iv) Chemical resistance, strength retained
after 72 h immersion
≥ 70 % IS 17363
NOTES
1 Molecular weight should be greater than 25 000 g/mol.
2 Carboxyl end groups 30 mmol/kg.
3 The design strength of reinforcement should be calculated as per Section 8.
4 The minimum strain requirements shall be satisfied as per Section 8 for a given application.
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28 POLYMERIC DRAINAGE PRODUCTS
28.1 Nonwoven geotextiles used for separation,
filtration and drainage functions shall be as per
IS 16362. Drainage geo-composites may also be
considered for drainage applications. Based on the
requirements and resistance to installation as per the
site condition, the geotextiles can be classified as
follows for various applications in reinforced soil
walls and slope applications.
28.2 A geo-composite drainage layer shall
comprise of a drain core with a geotextile filter
thermally bonded on both sides. The textile filters
shall have flap extending beyond the core on both
edges. The drainage composite used in separation,
filtration and drainage functions shall conform to the
requirements specified in Table 12, Table 13,
Table 14 and Table 15.
Table 12 Selection Criteria of Geotextile Class Based on Application
(Clauses 28.2 and 42.4)
Sl No. Type of Geotextile Application
(1) (2) (3)
i) Class 1 These should be used for separation applications where harsh
installation condition prevails such as surrounding the drainage
aggregate used as chimney drain between retained soil and reinforced
soil, slope applications etc.
ii) Class 2 These should be used where moderate installation condition prevails
such as:
1) Separating the reinforced fill (pond ash) and 600 mm
drainage bay in reinforced soil walls; and
2) RS wall panel joints.
iii) Class 3 These shall be used at less severe installation condition.
Table 13 Requirements of Drainage Composite
(Clause 28.2)
Sl No. Characteristics Requirement Tolerance Method of Test,
Ref to
(1) (2) (3) (4) (5)
i) Thickness at 2kPa, mm, Min 6 – IS 13162 (Part 3)
ii) Mass per unit area, g/m², Min 1 040 – IS 14716
iii) Tensile strength MD/
CMD, kN/m
20/20 - 10 Percent IS 16635
iv) CBR puncture resistance,
N, Min
3 000 IS 16078
v) Resistance to weathering To be covered with
soil for 14 days
IS 13162 (Part 2)
vi) Resistance to chemicals Excellent IS 17363
NOTE — Manufacturer has to provide test report for the factors, such as compression creep, chemical and biological clogging
and geotextile intrusion, to derive long term flow.
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Table 14 In-Plane Flow Requirements of Drainage Composite
(Clause 28.2)
Table 15 Requirements of Geotextile for Drainage Composite
(Clause 28.2)
Sl No. Requirement Tolerance, Percent Method of Test, Ref to
(1)
Characteristics
(2) (3) (4) (5)
i) Thickness at 2kPa, mm 1 - 20 IS 13162 (Part 3)
ii) Tensile strength MD/CMD,
kN/m
9.5/9.5 - 13 IS 16635
iii) Pore size; O90 µm 120 ± 30 IS 16237
iv) CBR puncture resistance, N 1 600 - 20 IS 16078
v) Dynamic perforation cone
drop, mm
32 + 20 IS 13162 (Part 4)
NOTE — The geocomposite drain shall be tested for UV resistance and oxidation. The samples shall be tested at reputed NABL
accredited geosynthetics testing laboratory, IITs etc. The report shall not be older than 5 years.
Example Calculation of Geocomposite Drain for
Vertical Drainage
Height of RS wall = 10 m
Permeability of soil (K) = 5 × 10-5
m/s (assumed,
for sandy soil)
Unit weight of backfill soil (ɣ) = 20 kN/m3
Coefficient of active earth pressure (Ka) = 0.5
Pressure at bottom of wall, P = Ka ɣ H = 0.5 × 20 ×
10 = 100 kPa
Assuming (Nf/Nd) = 1, where Nf and Nd are No. of
Reduction factor for retaining walls (as per Koerner,
page 873 Vol 2 Table 8.5)
For elastic deformation (RDIN) = 1.4
For creep resistance (RDCR) = 1.3
For chemical clogging (RDCC) = 1.3
For biological clogging (RDBC) = 1.25
Sl No. Confining Unit of
Measurement
In-plane Water
Flow MD (R/S) Hydraulic
Gradient - 1.0
In-plane Water Flow
MD (S/S) Hydraulic
Gradient - 0.1
Method of
Test, Ref to
(1) (2) (3) (4) (5) (6)
i) 20 litre/m.s 2.4 - 0.40 0.67 - 0.13 IS 17179
ii) 100 litre/m.s 1.95 - 0.33 0.53 - 0.11 IS 17179
iii) 200 litre/m.s 1.45 - 0.24 0.37 - 0.07 IS 17179
NOTES
1 S/S with soft/soft foam contact surfaces to simulate textile intrusion into the core due to soil pressure from both sides.
2 R/S rigid/soft contact surfaces to simulate conditions where composite is placed against rigid concrete surface on one side and soil on other side.
3 Placement of drainage composite shall be carried out at site by keeping machine direction in vertical direction.
Requirement Tolerance Requirement Tolerance
(6) (7)
flow line in both directions
Ultimate flow through soil (q) = K × H × (Nf/Nd)
= 5 × 10-5
× 10 × 1 = 0.5 litre/s.m
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Required flow rate = q × RF = 0.5 × 2.96 = 1.48 l/m.s
= 1.5 l/m.s (approx).
At i = 1 and 100 kPa pressure, the required flow
rate = 1.5 l/m.s.
NOTE — The reduction factors considered are for calculation
purpose only and the values may vary for different
geo-composite drains. The same shall be verified from the test
results of drainage composite by the manufacturer.
29 OTHER POLYMERIC PRODUCTS
The specifications of other polymeric products used
in reinforced soil structures shall conform to the
requirements specified in following table.
30 OTHER MATERIALS
30.1 Technical Specification of Welded Wire
Mesh Facing
30.1.1 Permanent Facing System
Galvanized welded mesh panels for permanent
facing shall be fabricated from minimum 8 mm
diameter steel bars manufactured and cold drawn as
per IS 7887 Grade 4 or SAE 1018 with yield strength
350 MPa, tensile strength 450 MPa, minimum
elongation 10 percent. Welding penetration at joints
of welded mesh panels shall be minimum 8 percent
of the combined diameter of the unwelded steel bars.
The weld penetration thus achieved shall provide
weld strength of minimum 12 kN. The welding shall
be done by automatic or semi-automatic electric
resistance welding process without using filler
wires. The weld strength of 12 kN shall be validated
by uniaxial weld test of samples taken randomly
from fabricated welded mesh panels. After welding,
the completed wire mesh panels shall be hot dip
galvanised for ensuring minimum zinc deposit of
500 gm per sqm (70 micron) as per IS 4759.
30.1.2 Sacrificial Welded Mesh for Temporary
Facing Support
Welded mesh panels for temporary support can be
fabricated from ungalvanized TMT/Mild steel bars
of minimum 8 mm diameter. The steel bars used to
fabricate temporary welded mesh panels shall be as
per specifications of the solution provider and shall
be appropriate for the temporary support function
and the working stress that the temporary facing is
anticipated to be subjected to. The temporary welded
mesh panels may be fabricated at factory or site by
means of suitable welding process.
30.2 Bearing Pad Specifications
Walls using segmental precast concrete panels
require bearing pads in their horizontal joints
(and diagonal, if applicable) that provide some
compressibility and movement between panels
during elastic compression and settlement of the
reinforced fill and preclude concrete-to-concrete
contact. These materials are generally ethylene
propylene diene monomer (EPDM) rubber pads or
HDPE. Two bearing pads are usually used on 1.5 m
wide panels and at least three bearing pads with 3 m
wide panels. A minimum of two bearing pads are
used per horizontal panel joint.
EPDM bearing pads shall meet the following
material requirements given Table 16.
30.3 Rolled Erosion Control Products (RECP)
RECPs generally used are made of biodegradable
natural fibres such as straw, jute, coir or wood
shavings (used individually or in combination)
stuffed into polymeric or organic nettings on either
side to form a mat or blanket like structure.
Obviously when mats are made using natural fibres,
they would be biodegradable also, but they don't
provide everlasting protection. RECPs are used in
combination with seed beds to enhance the
establishment of vegetation.
The RECP shall meet the requirements specified in
Table 17.
Field conditions like harsh areas/high survivability
requirements may warrant use of RECP mats with
tensile strength of 35 kN/m or more.
30.4 Others
All facings systems and facing units, including
connections between facings and reinforcement and
jointing materials, when these are needed, shall
conform with the specification for the works and
exhibit the long-term properties required by design.
The other materials used in reinforced soil structures
shall conform to the requirement as specified in
Table 18.
Sl No. Product Requirement
(1) (2) (3)
i) Perforated pipes for
carrying drainage
(perforations may be
done at site)
As per IS 15328
ii) Geomembrane
(barrier) HDPE
As per IS 16352
iii) Geocells (load
bearing applications)
As per
IS 17483 (Part 1)
iv) Geocells (erosion
protection of slopes)
As per
IS 17483 (Part 2)
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Table 16 Requirements of Bearing Pads
(Clause 30.2)
Sl No. Characteristics Requirement Method of Test, Ref to
(1) (2) (3) (4)
i) Base polymer EPDM –
ii) Colour Black Visual
iii) Grade, type and class of EPDM Grade 2, Type A, Class A ISO 4097
iv) Hardness (Sh.A) 80 ± 5 IS 13360 (Part 5/Sec 11)
v) Tensile strength (MPa), Min 12 IS 3400 (Part 1)
vi) Elongation at break, percent, Min 200 IS 3400 (Part 1)
vii)
Heat ageing at 70 °C for 70 h
Change in hardness, (points), Max ± 15 IS 3400 (Part 4)
Change in tensile, percent, Max ± 30
Change in elongation, percent, Max - 50
viii) Compression set at 70 °C for 22 h,
percent, Max
50 IS 3400 (Part 10/Sec 1
and Sec 2)
ix) Resistance to ozone, quality, retention
rating, percent, Min
85 IS 3400 (Part 20)
x) Water resistance for 70 h at 100 °C,
volume change, percent, Max
10 IS 3400 (Part 6)
xi) Max ash content, percent 8 ± 2 IS 11720 (Part 5)
Sl No. Characteristics Requirement Method of test,
(1) (2) (3)
Ref to
(4)
i) Tensile strength, kN/m, Min 2 IS 16635
ii) Mass, gm/m2
, Min 250 IS 14716
iii) Thickness at 2 kPa, mm, Min 6.5 IS 13162 (Part 3)
iv) UV resistance, strength retained
after 500 h exposure, percent
80 IS 17363
Table 17 Requirements of Other Materials Rolled Erosion Control Products
Used in Reinforced Soil Structures
(Clause 30.3)
–
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Table 18 Requirements of Other Materials Used in Reinforced Soil Structures
(Clause 30.4)
Sl No. Characteristics Requirement
(1) (2) (3)
i) Reinforced concrete panels
All units shall be free of cracks or defects that would interfere with
the unit's proper placing or significantly impair the structure's
strength or permanence
Concrete panels shall be made of minimum of M-35 concrete.
Minimum thickness of 160 mm (excluding architectural finish)
Minimum steel requirement as per IS 456
ii) Precast concrete modular blocks As per 33.1.3
iii) Soil bags for wraparound fascia As per manufacturer specifications
iv) Vegetation As per 44.3 (locally available should be preferred)
v) Levelling pad — PCC Plain cement concrete (PCC) with minimum strength of 15 MPa
vi) Steel/polymer connections to
geosynthetic
As per manufacturer specifications
vii) Gabion: woven wire mesh As per IS 16014 (for verticals faced and inclined units for reinforced
soil structures)
SECTION 4 DESIGN OF REINFORCED SOIL WALLS
31 SCOPE
This chapter deals with the design aspects of
reinforced soil wall systems for various soil
retaining applications.
32 GENERAL
32.1 Introduction
The reinforced soil retaining walls are structural
systems where in soils are internally stabilized by
the inclusion of discrete layers of reinforcing
elements which are generally placed horizontally
between successive lifts of fill during construction.
The soil and reinforcement behave as a coherent
composite mass and resist the earth pressures from
the retained soil and other externally imposed loads.
Reinforced soil structures with a face inclination
greater than or equal to 70° from horizontal are
generally considered as reinforced soil walls and
with a face inclination less than 70° from horizontal
are considered as reinforced soil slopes. These are
more economical solutions over their conventional
counterparts for example, reinforced concrete
retaining structures such as mass gravity walls,
RCC retaining walls etc.
32.2 Types of Reinforced Soil Walls
Reinforced soil walls are categorized as follows
based on the geometry, surcharge loads and other
significant external loads:
32.2.1 Simple Geometry
a) RS walls with horizontal backfill;
b) RS walls with sloping surcharge; and
c) RS walls with broken slope.
32.2.2 Complex Geometry
a) Bridge abutments with RS walls (Section 6
— Reinforced soil true abutments or any
strip loading cases);
b) Multi-tiered RS walls;
c) Trapezoidal RS walls;
d) Back-to-back RS walls;
e) Shored RS walls; and
f) Water Front RS walls.
32.3 Reinforced Soil Wall Applications
The reinforced soil walls are cost-effective
alternatives for applications compared to similar
height reinforced concrete and gravity retaining
walls. These includes approach to the structures such
as highways, flyovers, rail over bridge, vehicular
underpass and cattle underpass, bride abutments,
wing walls, temporary walls, waterfront structures
for river training, landscaping walls etc. These are
also suitable in areas where the right-of-way is
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limited due to which embankments with slopes
cannot be constructed.
33 REINFORCED SOIL WALL ELEMENTS
AND MATERIALS PROPERTIES
33.1 The typical cross section of reinforced soil
wall is shown in Fig. 4 which includes different
components of RS walls such as soil reinforcement,
reinforced fill, retained backfill, drainage media,
nonwoven geotextile, facing system, connection
system, levelling pad, coping beam, friction slab,
crash barrier and other accessories.
33.1.1 Reinforced Fill and Retained Backfill
Properties
Reinforced soil walls require high quality
granular fill for durability, adequate drainage,
constructability and soil reinforcement interaction.
The reinforced fill and retained backfill shall be well
graded, free from organic or other deleterious
materials and shall comply with the requirements
mentioned in Section 3 material.
33.1.1.1 Reinforced fill
33.1.1.1.1 Reinforced fill refers to the soil material
placed within the reinforcement zone in RS walls.
The proposed gradation of the fill ensures that it is
well graded, free draining and has adequate shear
strength once it is compacted.
33.1.1.1.2 Cohesion of the reinforced soil fill is
neglected in the design. The maximum effective
design friction angle shall be limited to 34°.
33.1.1.1.3 For metallic reinforcement or metallic
connection system, it should be ensured that
electro-chemical properties of the fill are
satisfactory and would not cause or trigger corrosion
of the reinforcement. Metallic reinforcement should
not be used for soils with a resistivity of less than
1 000 ohm cm. The fill electro-chemical properties
shall be as per Section 3 material.
33.1.1.1.4 The compaction specifications should
include a specified lift thickness and allowable range
of moisture content with reference to optimum.
Compaction moisture control should be ± 2 percent
of optimum moisture content. The compaction
properties are to be determined from modified
proctor compaction tests using heavy compactor.
FIG. 4 TYPICAL CROSS SECTION OF REINFORCED SOIL WALLS
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33.1.1.1.5 Pond ash can also be used as a fill material
in RS walls. The properties for the pond ash as fill
shall be in accordance to the specifications as given
in Section 3 material of code of practice.
33.1.1.2 Retained backfill
33.1.1.2.1 The key properties required for retained
backfill are the strength and unit weight based on
evaluation and testing of subsurface or borrow pit
data. As with reinforced fill, a cohesion value of zero
is conservatively recommended for the long-term,
effective strength of the retained backfill.
The strength properties are required for the
determination of the coefficient of earth pressure
used in design as well as overall stability analysis. In
addition, the groundwater levels above the proposed
base of construction must be determined to evaluate
hydrostatic stresses in the retained zone and plan an
appropriate drainage scheme to control ground water
conditions.
33.1.1.2.2 It is recommended that same material
shall be used for retained fill as that of reinforced fill
that is the properties of the retained backfill shall be
same as those for the reinforced fill materials as per
Section 3. In case if significant amount of retained
backfill is required, the minimum internal friction
angle shall be relaxed to 25° and plasticity index
shall be less than equal to 20. In case of retained
backfill with different soil properties that the
reinforced fill, the design shall be done considering
the actual properties of reinforced fill and retained
backfill.
33.1.1.2.3 If reinforced fill material is pond ash, the
same material must be used for retained backfill.
33.1.1.2.4 In case of existing natural ground or
slope, the retained mass might not be purely
cohesionless. In such situations, drainage
blanket/chimney drainage/geo-composite drain shall
be provided between the reinforced soil zone and
retained soil as per the specifications given in
Section 3.
33.1.2 Soil Reinforcement: Extensible and
Inextensible Reinforcement
The reinforcement for RS walls includes metallic
and polymeric type of reinforcements. Based on the
stress/strain behaviour of the reinforcing elements
these are typically classified into extensible and
inextensible reinforcements. Relevant IS codes as
mentioned in Section 3 material shall be referred
for the specifications of soil reinforcements. The
tests (tensile strength and elongation of soil
reinforcement) related to the soil reinforcement
shall be performed at an independent accredited
laboratory which is accredited by a competent
authority.
33.1.2.1 Extensible reinforcement
Reinforcements that sustain the design loads at
strains greater than 1 percent. Types of
reinforcements includes polyester uniaxial geogrid,
polymeric straps, geotextiles etc. The strength of
polymeric reinforcement is affected by temperature
and time. Therefore, it is important that the strength
is evaluated considering these two factors. The
tensile strength shall be evaluated by conducting
wide width tensile test as per relevant test method.
33.1.2.2 Inextensible reinforcement
Reinforcement that sustains the design loads at
strains less than or equal to 1 percent. Types of
reinforcement includes metallic strips, grids and
plates. In order to meet the design life, the metallic
reinforcement shall be coated with zinc to delay
exposure and corrosion. The zinc coating shall
confirm to relevant IS code. A sacrificial thickness
of minimum 0.50 mm shall be provided on all sides
which designing.
For inextensible reinforcements (metallic
reinforcements), coherent gravity method is being
followed for the design of reinforced soil walls. This
method is based on the monitored behaviour of
structures using inextensible reinforcements and has
evolved over a number of years from observations
on a large number of structures, corroborated by
theoretical analysis.
33.1.3 Facing Systems
33.1.3.1 Facing is an important component of
reinforced soil systems. Facings such as full height
panels, discrete/segmental concrete panels, modular
concrete blocks, welded wire grid, woven steel wire
mesh, gabions and wrap around systems are
commonly used for reinforced soil structures.
Following are the major functions of the facings:
a) Prevention of localized failures that is
ravelling of fills between reinforcement
layers and erosion control in slopes;
b) Flexible to accommodate deformations up
to some extent;
c) Temporary formwork;
d) Ease of construction; and
e) Architectural finish.
33.1.3.2 The facing shall be designed to withstand
stresses which typically includes normal stresses
arising due to panels/blocks above it and forces and
moments arising from connections to soil
reinforcement.
33.1.3.3 The chosen facing should be compatible
with the extensibility of reinforcement.
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Compatibility to ensure flexibility of the system
should be attained by choosing an appropriate
combination of facing and the reinforcement.
33.1.3.4 Concrete panels should be of minimum
M35 concrete strength. The minimum thickness of
the panels shall be 160 mm (excluding any
architectural finishing). The reinforcement design of
facing panels shall comply with the requirements as
given in the subsequent sections of this chapter
which is in line with IS 456.
33.1.3.5 Modular blocks should be manufactured
using a block making machine and cast from a
cement sand mix to attain a minimum concrete
strength (M35) of 35 N/mm2
. In case of blocks, the
hollow area shall not exceed 40 percent of the
cross-sectional area. The outer side of the block shall
have a minimum thickness of 85 mm and inner side
45 mm. Blocks may also be profiled to create
hollows between adjacent blocks. The hollow space
shall be filled with clean, 20 mm down sound
aggregate to add to friction between the reinforcing
grid and facing blocks. The manufactured blocks
and panels should have consistency in dimensions
and shapes.
33.1.3.6 Connection between the facing and the soil
reinforcement shall be done by using appropriate
connector which is compatible with the type of the
reinforcement and the facing system. In general, the
connectors used are nut or bolt, HDPE inserts with
bodkin joint, hollow embedded devices,
polymeric/steel rods or any other type of proven
arrangement which is experimentally tested and
proven well. Connections of the facing element and
the soil reinforcement should be clearly defined and
tested appropriately in accredited testing facilities.
33.1.4 Drainage Considerations
33.1.4.1 In normal conditions in order to ensure that
no hydrostatic as well as pore pressure is developed
in the reinforced soil structure, adequate drainage
measures need to be taken. A drainage bay of
minimum 600 mm width at the back of the facing
shall be provided as an adequate drainage measure.
Additionally, the aggregates shall not be friable,
flaky, elongated and are sound in strength. The
materials shall meet the requirements as described
in Section 3 materials.
33.1.4.2 Alternatively, drainage composite with
combination of drainage bay of 300 mm shall be
provided behind the facing of RS walls for ensuring
adequate drainage. However, it is not recommended
to use drainage composite when pond ash is used as
reinforced fill. In case of pond ash, 600 mm wide
drainage bay shall be used and a non-woven
geotextile shall be provided as a separation/filtration
layer between the drainage aggregates and the
reinforced fill material.
33.1.4.3 A chimney drain should be provided
between the retained backfill and the reinforced fill
to ensure proper drainage wherever RS walls are
provided to support cohesive retained soil with
higher fine (specifically clay) content. The chimney
drain should be designed to carry the discharge and
should be provided vertically at the back of the
reinforced fill and continued in a horizontal extent to
a depth well below the toe of the RS wall and lead
to a drain meant to carry the discharge away from
the RS wall.
33.1.4.4 The risk due to water and the extent of
drainage measures required will depend on the type
of the reinforced soil structure and the severity of its
exposure to water:
a) Reinforced soil structures which are above
ground water table and above high flood
levels: examples include embankments in
sites not affected by floods and hill side
fills where the ground water table is
permanently below the founding level of
the reinforced soil structure. The main
source of water in these structures is
infiltration of rain water or snow melt from
the surface or from leaking pipes;
b) Hill side fills with high water table
conditions: where the ground water table
can rise above the founding level of the
reinforced soil structures, relatively large
volumes of water may enter the reinforced
fill and design of drainage measures should
cater to this;
c) Reinforced soil structures which are likely
to be partially submerged: reinforced soil
structures located in flood-prone sites may
be subjected to partial submergence during
the floods. Design should consider the
effects of higher hydrostatic pressures and
sudden draw down; and
d) Reinforced soil structures exposed to water
bodies: bridge approach embankments and
reinforced soil walls/slopes supporting
the banks of water bodies like
rivers/streams/canals/ponds/reservoirs may
be subject to periodic submergence up to
the high water level and may be impacted
by water currents. The effects of
hydrostatic pressures, seepage pressures,
scour, internal erosion and piping should be
carefully evaluated and appropriate counter
measures provided.
33.1.4.5 The various approaches to minimize the
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effects of water include:
a) Proper surface drainage measures to collect
and dispose of the surface runoff;
b) Use of impervious barriers to minimize the
infiltration of surface water into the
c) Use of fill with sufficient permeability to
quickly remove the water entering into the
reinforced soil structure and dissipate the
excess pore water or hydrostatic pressures;
d) Provision of adequate subsurface drainage
arrangements including granular/
geosynthetic drains, perforated pipes, panel
drains etc;
e) Designing for anticipated excess pore-
water pressures or hydrostatic pressures
including the effects of sudden drawdown;
f) Provision of appropriate granular or
geotextile filters to prevent internal erosion
and piping; and
g) Protection against scour through adequate
embedment and using scour protection
aprons.
Guidance for design and detailing of drainage
measures is provided in Section 9.
33.1.4.6 The details of other RS wall components
such as friction slab, crash barrier, coping beam,
vertical construction joints etc shall be as per design
and drawing. The drawing detailing of such
components shall be referred from Section 10
detailing and construction.
34 DESIGN
34.1 Design Philosophy
34.1.1 The aim of design is to achieve an acceptable
probability that any structure being designed will
perform satisfactorily during the intended service
life of the structure. Therefore, the design
philosophy shall include the design procedure for
durability, construction and use in service as a
whole. The reinforced soil wall (RSW) shall sustain
all the loads and deformations of normal
construction and use, adequate durability and
resistance to the extreme events which might occur
in the design life of the structure based on the
geophysical condition of the location of the
structure. The safe, serviceable and durable design
of a structure does not result only from design
calculations, due considerations shall be given to the
properties of the materials, proper detailing of the
structural components, good construction practice
and workmanship, quality control, inspection during
construction and maintenance of the structure which
are also equally important. This design chapter has
been written on the assumptions that the
aforementioned points are properly followed as per
the code of practice.
34.1.2 In the past, reinforced soil walls were
designed using various design methods such as
allowable stress design, limit state design, limit
equilibrium methods etc. Although these
conventional design methods based on factor of
safety can provide a basis for a safe design, load and
resistance factor design approach, being a much-
advanced limit state method is being followed in this
code of practice for the design of reinforced soil
walls.
34.2 Load and Resistance Factor Design (LRFD)
Overview
34.2.1 Load and resistance factor approach is latest
design methodology adopted for the design and
analysis of structures. This design philosophy has
been gaining ground in areas of structural
engineering practice in many parts of the word such
as India, United States, Canada, Europe etc for
example, the euro code for soil retaining structures
uses the limit state design methodology, which is
very similar to the LRFD methodology.
34.2.2 LRFD method is based on the principle that
the strength (resistance) of various materials is
scaled down by some factors while the applied loads
are scaled up by some factors, and thereby the
structural elements are designed using reduced
strength and increased loads. The strength of
materials considered for design is the ultimate
strength, which results in utilization of elastic,
plastic and strain hardening stages of material
thereby giving economical and safe design
consistently. The factors by which strength is
reduced depends on the confidence of predictability
of strength of the material. Similarly, load factors are
more for those loads which are highly unpredictable
than loads which can be more accurately predicted.
Thus load factor for dead load is less than that for
live load or wind load as dead load will not vary as
much as live or wind loads. Further, LRFD method
also considers serviceability limits like maximum
allowable deflection, settlement etc in addition to
the strength design.
34.2.3 Regardless of the design methodology, the
fundamental analytical methods for reinforced soil
walls such as external and internal stability
evaluation remain unchanged. The primary change
is in the way the loads and resistances are compared
and how the uncertainty is incorporated into the
design procedure.
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34.3 Definitions of Loads and Load Combinations
34.3.1 The applicable loads which shall be account
for the design of RSW are as follows:
a) Dead load;
b) Live load (traffic);
c) Strip load (imposed load);
d) Earthquake load;
e) Hydrostatic load; and
f) Impact load.
34.3.2 These loads are categorized as permanent and
transient. The abbreviations and definitions of
different loads which are considered for the design
of reinforced soil walls are shown in Fig. 5 and
summarized in following table:
34.3.3 An example of an ES load on RS wall is the
pressure from a spread footing above the reinforced
mass. An example of EV load is a sloping fill above
the top of RS wall and weight of reinforced soil
zone.
34.3.4 As per IRC : 78, 710.6.9 live load due to
traffic (qT) is considered equivalent to 1.2 m of the
earth fill. The minimum value of live load shall be
24 kPa. qT refers to traffic load.
34.3.5 For railways, airports and aviation projects,
etc the live load values shall be increased
accordingly considering the heavy axle load.
arrangement. This load shall be categorized under
ES type loading.
34.3.7 For most RS wall designs, strength limit
states control the member sizes. Service limit state
may control aspects such as joint width openings and
construction sequences based on the anticipated
deformations.
34.3.8 Extreme events may affect both member sizes
as well as deformations. The extreme events that
require due consideration in the design of reinforced
soil walls are earthquake, vehicular impact and flood
or scour condition.
34.3.9 Based on the strength and service criteria,
reinforced soil walls are designed for the following
load combinations:
a) Strength I;
b) Service I;
c) Extreme event I (seismic event);
d) Extreme event II (vehicular impact event);
and
e) Extreme event III (flood event and scour).
34.3.10 The extreme event load combinations are
checked based on the location of the structure or the
event that may happen in future. The load factors
which shall be used for different load combinations
are discussed later in this chapter.
34.4 Mode of Failures and Performance Criteria
34.4.1 Reinforced soil wall may fail in the following
three modes that is, external, internal and compound.
In load and resistance factor design (LRFD), the
external and internal stability of the reinforced soil
wall are evaluated at strength limit states and overall
stability and wall movements are evaluated at the
serviceability limit state. These different modes of
failure are related to the failure of the reinforced soil
zone as follows:
a) External: The failure surface is located
outside the reinforced soil zone;
b) Internal: The failure surface is located
inside the reinforced soil zone; and
c) Compound: The failure surface is located
partly inside and partly outside the
reinforced soil zone.
34.4.2 External stability is evaluated by assuming
the reinforced soil zone as a coherent mass with
lateral earth pressure acting on the back side of the
block. The three external stability modes of failure
involve the check for following potential failure
mechanisms (see Fig. 6):
a) Sliding on the base;
Permanent Loads
EH Earth pressure on reinforced soil zone
due to retained soil mass
ES Crash barrier-friction slab load or
w-beam load as a strip footing, etc
EV Vertical pressure or weight of
reinforced soil zone, sloping
surcharge weight, dead load due to
pavement layers, etc
Transient Loads
CT Impact load on barriers
EQ Earthquake load (seismic load)
LS* Live load surcharge/vehicular live
load (traffic load)
34.3.6 In addition to the applicable loads as
mentioned in Table 24, if the gap slap pedestal is
resting on the reinforced soil wall. The dead load
due to the gap slab and the pedestal shall also be
considered in the load calculation for the design of
reinforced soil wall based on the span length and
geometry of the gap slab and pedestrian
arrangement. This load shall be categorized under
ES type loading.
b) Limiting eccentricity; and
c) Bearing capacity.
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FIG. 5 DIFFERENT APPLICABLE LOAD TYPES ON REINFORCED SOIL WALLS
FIG. 6 POTENTIAL EXTERNAL FAILURE MECHANISM OF REINFORCED SOIL WALLS
ES (crash barrier-friction
slab load) EV (vertical load due to soil weight, sloping surcharge load, load due to
pavement layers, etc).
IS 18591 : 2024
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EH (lateral soil
pressure)
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34.4.3 Internal Stability mode involves the failure of
reinforcement and depends on mainly three factors
that is tensile resistance of reinforcement against
rupture, soil-reinforcement interaction for pull out
and internal sliding.
34.4.4 Global stability analysis and compound
stability analysis of the reinforced soil wall shall be
performed to check for any external failure mode
and for any internal failure mode other than the
aforementioned failure mechanism of external and
internal stability.
34.4.5 The factored resistance and the factored loads
for different checks are computed and the design is
considered safe if the ratio of the factored resistance
to that of the factored load is greater than 1. This
ratio is termed as capacity to demand ratio (CDR).
The lateral and vertical wall movements should be
within the limits as stated later in the design
procedures.
34.5 Design Procedures
The basic design parameters, steps, and analysis for
reinforced soil wall are listed in Table 19. These
steps are for walls with simple geometry. Additional
considerations shall be given for the design of walls
with complex geometries such as superimposed RS
walls, true abutments etc see Fig. 18.
Table 19 Basic Design Steps for Reinforced Soil Walls
(Clause 34.5)
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Establish project requirements
Establish project parameters
Initial sizing: Wall embedment depth, design height, minimum reinforcement length and
vertical spacing of reinforcement
Coefficient of lateral earth pressure
Nominal load calculations
Summary of load factors and resistance factors
External stability analysis
a) Evaluate direct sliding
Evaluate eccentricity
Evaluate bearing capacity
b)
c)
Step 8 Internal stability analysis
a) Geometric characteristics of soil reinforcements
b) Coverage ratio calculation
c) Reinforcement layout
d) Potential failure surface
e) Define unfactored loads
f) Calculate factored tensile forces in the reinforcement layers
g) Calculate soil reinforcement resistance
h) Internal stability with respect to rupture
Internal stability with respect to pullout or adherence
Check for internal sliding
j)
k)
Step 9
Step 10
Step 11
Check for connection strength and design of facing elements
Check for settlements, vertical and lateral wall movements
Slope stability analysis (global stability and compound stability analysis)
(1) (2) (3)
i)
ii)
iii)
iv)
v)
vi)
vii)
viii)
ix)
x)
xi)
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34.6 Project Requirements
The requirements of the project such as wall design
height, batter angle, backslope and toe slope, loading
conditions, performance criteria, and construction
constraints must be defined prior to proceeding with
the design.
34.7 Project Parameters
The following parameters must be defined or
provided by the client or the contractor based on the
properties discussed in the code of practice and
other relevant references for the Reinforced soil
walls:
a) Existing topography of the location;
b) Subsurface conditions across the site and
appropriate geophysical investigation;
c) Reinforced fill: engineering properties of
the reinforced fill material;
d) Retained backfill: engineering properties of
the retained backfill, addressing all
possible fills that is, in situ, imported,
onsite, etc; and
e) Seismic zone of the project location.
The engineering properties of the reinforced fill and
retained backfill shall be as per the descriptions in
Section 4 and Chapter 3 on materials.
34.8 Initial Sizing: Wall Embedment Depth,
Design Height, Minimum Reinforcement Length
and Vertical Spacing of Soil Reinforcements
34.8.1 Wall Embedment Depth
34.8.1.1 The toe of the wall shall be embedded
below the ground surface. The required embedment
depth shall be decided based on various factors such
as vertical pressure imposed on foundation, erosion
and scour, slope geometry at the toe, presence of
drains adjacent to the toe and risk of exposure of the
toe due to subsequent excavation. The minimum
embedment depths shall not be less than those
listed in Table 20.
Table 20 Minimum Embedment Depths for
Reinforced Soil Walls
(Clause 34.8.1.1)
Sl No. Slope in Front of
Wall
Minimum Depth
(d) to Top of
Levelling Pad
(1) (2) (3)
i) All geometries 1 000 mm
minimum
ii) Horizontal (walls) H/20
Sl No. Slope in Front of
Wall
Minimum Depth
(d) to Top of
Levelling Pad
(1) (2) (3)
iii) Horizontal
(abutments)
H/10
iv) 3H : 1V H/10
v) 2H : 1V H/7
vi) 1.5H : 1V H/5
34.8.1.2 It shall be noted that larger embedment
depths may be required depending on shrinkage and
swelling of foundation soil, seismic activity and
scour. A larger embedment depth may also be
required based on bearing, settlement and global
stability calculations. In case of possibility of scour,
the embedment depth should be below the maximum
estimated scour depth. Embedment is usually not
required for RS walls founded on rocks.
34.8.1.3 A minimum horizontal bench of 1.2 m
width measured from the facing shall be provided
in front of walls founded on slopes as shown in
Fig. 7 (B) This bench is intended to provide
resistance against bearing failure and to provide
access for maintenance inspections.
34.8.2 Design Height (H)
The full height of the reinforced soil wall considered
for design is the sum total of embedment depth and
the final exposed height of the wall up to the top of
the facing unit as shown in Fig. 4.
34.8.3 Minimum Reinforcement Length
The minimum length of reinforcement to initiate
the design shall be greater of 0.7 H or 3.0 m, (where
H is the design height of the RS wall). This initial
length is checked for internal and external stability
calculations and shall be increased accordingly. In
general, the geometrical distribution of soil
reinforcement shall be as per Fig. 4. In some
specific cases, the top few layers of reinforcement
will require higher length for pull out internal
stability requirements. In some cases, bottom most
reinforcement layer will require higher length of
reinforcements for internal sliding. In such situation
the bottom most reinforcement shall be increased
and the geometrical distribution of the few bottom
layers shall satisfy the criteria as shown in Fig. 8.
Structures with sloping surcharge and broken back
slope usually require longer reinforcements often of
the order of 1.0 H or higher.
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34.8.4 Vertical Spacing of Soil Reinforcements
The spacing of reinforcement shall be established
based on the design principles. The general practice
is to keep the vertical spacing constant and increase
the density of reinforcement with depth by
increasing the coverage ratio of reinforcement.
However, the criteria of constant spacing may be
relaxed in situations as per the structure
requirements. The vertical spacing of the primary
reinforcement shall not be greater than 800 mm for
all types of facing systems (example: segmental/
discrete panels, gabion mesh units etc) and for all
types of soil reinforcements (example: geogrids,
geostrips, metallic reinforcements etc) in order to
provide a coherent reinforced soil mass. Depending
upon the type and dimensions of facing units, the
vertical spacing may be limited to a lower value to
satisfy the stability of RS walls. However, the
criteria of maximum vertical spacing of
reinforcement is limited to 800 mm. RS walls with
modular blocks where the connection capacity is by
friction, the maximum vertical spacing of
reinforcement shall be minimum of twice the block
depth (measured from front face of block to the rear
face of block) or 600 mm. In case of wrap around
facing RS walls, the maximum spacing shall not be
greater than 500 mm to avoid bulging.
34.9 Earth Pressure Coefficient Calculation
34.9.1 The horizontal earth pressure exerted by the
retained fill on the reinforced fill zone shall be
considered as shown in Fig. 9.
(A)
(B)
FIG. 7 RS WALL EMBEDMENT REQUIREMENTS (A) LEVEL TOE CONDITION AND (B) BENCHED SLOPE TOE
CONDITION (D = MINIMUM DEPTH FOR HORIZONTAL SLOPE AND ds = MINIMUM DEPTH FOR SLOPING TOE)
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FIG. 8 GEOMETRIC REINFORCEMENT DISTRIBUTION CRITERIA OF RS WALL
FIG. 9 EARTH PRESSURE INCLINATION (Δ) FROM HORIZONTAL
.
∆ ≥ 2∆
qT
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34.9.2 The horizontal earth pressure coefficient shall
be calculated as per the Coulomb’s Expression as
given below:
….. (4-1)
where
 = nominal slope of backfill behind wall
f = angle of friction between retained
backfill and reinforced soil, set equal
to  (degrees);
ɸ = effective friction angle of retained
backfill (degrees); and
θ = 90° for vertical, or near ( 10°)
vertical wall (degrees).
FIG. 10 WALL INCLINATION ANGLE
34.9.3 In case of inextensible reinforcements
(metallic reinforcements), the horizontal earth
pressure exerted by the retained backfill on the
reinforced fill zone acts at an angle δ from the
horizontal as shown in Fig. 10. In case of extensible
reinforcements, the inclination of horizontal earth
pressure (δ) shall be considered as zero.
34.9.4 In case of coherent gravity method, the
inclination of horizontal earth pressure is expressed
by the following equation:
….. (4-2)
34.9.5 Alternatively, for extensible reinforcement
(polymeric reinforcements), the active earth
pressure expression for horizontal backslope and
near vertical RS wall can be computed as per the
following expression:
where
ɸ b = effective friction angle of retained
backfill (degrees).
34.9.6 Based on the geometry of the RS wall, the
above-mentioned Coulomb’s expression can be
considered for earth pressure computation with
appropriate modifications. Some of the cases are
discussed below for different RS wall geometries:
Case 1: Vertical wall and a sloping backfill — The
active coefficient of earth pressure shall be
calculated as per Coulomb’s Expression in equation
(4-1) for near-vertical walls (defined as walls with a
face batter of less than 10° from vertical) and a
sloping backfill.
NOTE — The earth pressure force, (FT) in Fig. 12, is
oriented at the same angle as the backslope, β, as it is
assumed that δ = β.
Case 2: Vertical wall with broken backslope — The
active earth pressure coefficient for this condition is
computed using equation (4-1), with the design
β angle and the interface angle δ both set equal to I,
as defined in Fig. 13.
Case 3: Battered wall with or without backslope —
For an inclined front face and reinforced zone (that
is batter) equal or greater than 10 degrees from
vertical, the coefficient of earth pressure can be
calculated using above equation where θ is the face
inclination from horizontal, and β the surcharge
slope angle as shown in Fig. 14. The wall friction
angle δ is assumed to be equal to β.
34.10 Nominal Load Calculations
34.10.1 The applicable loads for reinforced soil
walls are defined in Section 4. Loads for reinforced
soil wall includes earth pressure on reinforced soil
zone due to retained soil mass (EH), crash barrier-
friction slab load or w-beam load as a strip footing,
footing resting on RS wall etc (ES), vertical pressure
or weight of reinforced soil zone (EV), sloping
surcharge weight (EV), dead load due to pavement
layers (EV) and Live Load surcharge (LS) that is,
traffic load (qT). Loads due to earthquake and water
if applicable shall also be evaluated and the stability
shall be checked with appropriate load combinations
as mentioned in Section 4.



F
IS 18591 : 2024
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(degrees);
Kab =
sin2 (θ + ɸb
)
[1+√
sin (ɸb
+ f) sin (ɸb
− β)
sin (θ − f) sin(θ + β)
]
2
sin2θ sin(θ − f)
𝐾𝑎𝑏 = 𝑡𝑎𝑛2
(45 −
ɸ𝑏
) ... (4-3)
2
𝛿 = (1.2 −
𝐿
𝐻
) ɸb
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34.10.2 The load calculations depend on the
geometry of the reinforced soil wall. The nominal
(unfactored) load calculations for RS wall with
horizontal backslope with extensible reinforcement
is shown in Fig. 11. In case of inextensible
reinforcement, the lateral earth pressure acts at an
angle δ from horizontal as discussed in Section 4
(Fig. 10).
34.10.3 Fig. 12 and Fig. 13 show the earth pressure
developed on the vertical plane at the back end of
the reinforcements (both extensible and inextensible
reinforcements) for RS walls with sloping backfill
and broken backslope geometry respectively.
Reinforced soil wall with a batter of greater than
10° from the vertical is shown in Fig. 14.
34.11 Load Factors and Resistance Factors
34.11.1 The load factors for different loads and
load combinations as discussed in Section 4 are
mentioned in Table 21 and Table 22. The load
factors to use for simple geometry RS walls for
external stability calculations are illustrated in
Fig. 15 and Fig. 16. The maximum EV load factor
should be used for internal stability calculations.
34.11.2 Live loads are not used on specific design
steps since they contribute to stability. These are
identified in subsequent design steps.
FIG. 11 EXTERNAL ANALYSIS: NOMINAL EARTH PRESSURES; HORIZONTAL BACKSLOPE WITH TRAFFIC
SURCHARGE
q
q
qT H Kab
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FIG. 12 EXTERNAL ANALYSIS: EARTH PRESSURE; SLOPING BACKFILL CASE
FIG. 13 EXTERNAL ANALYSIS: EARTH PRESSURE WITH BROKEN BACK SLOPE AND TRAFFIC SURCHARGE
x
IS 18591 : 2024
41
2 2 2 2
𝑉2 =
𝛾r 𝐿 (ℎ − 𝐻)
if x = L; 𝑉2 =
𝛾r 𝑥 (ℎ − 𝐻)
+
𝛾r (𝐿 − 𝑥) (ℎ − 𝐻)
if x L; 𝑉2 =
𝛾r 𝑥 (ℎ−𝐻)
if x L
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FIG.14 NOTATION FOR COULOMB ACTIVE EARTH PRESSURES USED WITH BATTER, θ, GREATER THAN 100°
MEASURE FROM HORIZONTAL IN CLOCKWISE DIRECTION
Table 21 Typical Reinforced Soil Wall Load Combinations and Load Factors
(Clauses 34.11.1 and 35.2.1)
Sl No. Load Combination
Limit State
EH
ES
EV
LL
LS
Use One of These at a Time
EQ CT
(1) (2) (3) (4) (5) (6)
i) Strength I γp 1.75 – –
ii) Extreme event I γp γEQ 1.00 –
iii) Extreme event II and
Extreme event III
γp 0.50 – 1.00
iv) Service I 1.00 1.00 – –
NOTES
1 γp = load factor for permanent loading. May subscript as γP-EV, γP-EH, etc.
2 γEQ = load factor for live load applied simultaneously with seismic loads
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(Clause 34.11.1)
Sl No. Type of Load Load Factor
Maximum Minimum
(1) (2) (3) (4)
i) DC: Component and attachments 1.25 0.9
ii) EH: Horizontal earth pressure
1.5 0.9
iii) EV: Vertical earth pressure
a) Overall stability
b) Retaining walls and abutments
1.00
1.35
N/A
1.00
iv) ES: Earth surcharge 1.5 0.75
FIG.15 TYPICAL LOAD FACTORS FOR SLIDING STABILITY AND ECCENTRICITY CHECK
FIG.16 TYPICAL LOAD FACTORS FOR BEARING CALCULATIONS
γEV−MIN = 1.00
γEH−MAX = 1.50
γEV−MIN = 1.35
γEH−MAX = 1.50
43
a) Active
Table 22 Typical Reinforced Soil Wall Load Factors for Permanent Loads, γp
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34.11.3 The resistance factors for the external
stability analysis of reinforced soil walls are listed
in Table 23.
Table 23 External Stability Resistance Factors
for Reinforced Soil walls
(Clause 34.11.3)
Sl No. Stability
Mode
Resistance
Factor
(1) (2) (3)
i) Sliding 1.0
ii) Bearing 0.65
34.12 External Stability Analysis
As with conventional gravity and semi gravity
retaining structures, following are the potential
external failure mechanisms are usually considered
in sizing reinforced soil walls which are:
a) Direct sliding along the base;
b) Limiting eccentricity; and
c) Bearing capacity check.
34.12.1 Evaluate Direct Sliding
34.12.1.1 Sliding resistance along the base of the
wall is evaluated using the same procedures as for
spread footing on the soil. The live load surcharge is
not considered as a stabilizing force when checking
sliding, that is, the sliding stability check only
applies the live load above the retained backfill. The
driving force generally include factored horizontal
loads due to earth, water, seismic and surcharges.
The factored resistance against failure by sliding
(RR) can be estimated by:
…..(4-4)
where
resistance between soil and
foundation (equal to 1.0 for sliding
of soil-on-soil, see Table 24); and
R
= nominal sliding resistance between
reinforced fill and foundation soil.
34.12.1.2 Calculation steps and equations to
compute sliding for two typical cases are as follows:
a) Calculate nominal thrust, per unit width,
acting on the back of the reinforced zone;
Case 1: Wall with horizontal backslope:
(see Fig. 11)
…..(4-5)
F1 =
2
Kab γb H2
For a uniform surcharge, the resultant is:
..…(4-6)
where
Kab = active earth pressure coefficient for the
retained backfill;
b = unit weight of the retained backfill soil;
H = height of the retaining wall; and
qT = uniform live load surcharge = (γr )(ℎ. )
or minimum 24 kPa.
Case 2: Wall with sloping backfill: (see Fig. 12)
Calculate nominal retained backfill force resultant
per unit width, FT
….. (4-7)
where
Kab = active earth pressure coefficient for
the sloping backfill;
h = total height of wall, H and slope at
the back of the reinforced zone; and
= H + L tan β
Case 3: Wall with broken backslope: (see Fig. 17)
Calculate nominal retained backfill force resultant
per unit width, FT
……(4-8)
where
Note that these equations should be extended to
include other loads and geometries, for other cases,
such as additional traffic surcharge and pavement
layers loads.
b) Calculate the nominal and factored
horizontal driving forces. For a horizontal
Kab = active earth pressure coefficient
for the broke backslope;
h = total height of wall, H, and slope
at the back of the reinforced
zone;
= H + L tan β; if H + L tan β ≤
(H + S); S is height of broken
backslope; and
= H + S; if L tan β S.
IS 18591 : 2024
44
F2 = Kab qT H
The retained backfill resultant, F1, is:
FT = Kab γb h2
1
2
FT = Kab γb h2
1
2
RR = ϕ R
 
ϕ= resistance factor for shear 
1
γb
γb
γb
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backslope and uniform live load surcharge:
Σ F = F1 + F2
….. (4-9)
Pd = γEH F1 + γLS F2 …..(4-10)
....(4-11)
Use the maximum EH load factor (= 1.5) in these
equations because it creates the maximum driving
force effect for the sliding limit state.
c) Determine the most critical frictional
properties at the base and choose the
minimum soil friction angle from the three
possibilities as follows:
1) Sliding along the foundation soil, if its
shear strength (based on effective
stress parameters cfd + tan ɸfd, or total
stress parameters that is, undrained
condition for fine grained soils
cfd + tan ɸfd) is smaller than that of
reinforced fill material shear strength;
2) Sliding along the reinforced fill (ɸr);
and
3) For sheet type reinforcement, sliding
along the weaker of the upper and
lower soil-reinforcement interfaces.
The soil-reinforcement friction angle
ρ, should be measured by means of
interface direct shear tests. In the
absence of testing, it may be taken as
2/3 tan ɸr.
d) Calculate the nominal components of
resisting force and the factored resisting
force per unit length of the wall. For a
horizontal backslope and uniform live load
surcharge, the live load is excluded since it
increases sliding stability:
….(4-13)
For a sloping backfill condition:
Rr = [γEV (V1 + V2) + γEH (FT sinβ)] × µ ….(4-14)
where
 = minimum of tangent soil friction angle ɸ
’
’
[tan ɸfd, tan ɸr, or (for continuous
reinforcement) tan ρ].
External loads that increase sliding resistance should
only be included if those loads are permanent.
Minimum load factors should be used in the above
equation as it results in minimum resistance for the
sliding limit state.
e) Compare factored sliding resistance, Rr, to
the factored driving resistance to check that
the resistance is greater; and
f) Check the capacity demand ratio (CDR) for
sliding, CDR = Rr/Pd. If the CDR 1.0,
increase the reinforcement length, L and
repeat the calculations.
34.12.2 Evaluate Eccentricity
34.12.2.1 The system of forces for checking the
eccentricity at the base of the wall is shown in
Fig. 17. The eccentricity limit is checked by
applying the live load above the retained backfill
only as shown in Fig. 11. The influence of live load
(over reinforced soil zone) for resistance calculation
is ignored. The eccentricity, e, is the distance
between the resultant foundation load and the center
of the reinforced zone (that is, L/2) as illustrated in
Fig. 17. The eccentricity, e can be obtained from the
following equation:
….(4-15)
where
MD = destabilizing moment;
MR = resisting moment; and
V = vertical load.
34.12.2.2 Equations to compute eccentricity for two
typical cases are as follows:
Wall with horizontal backslope
Calculation steps for the determination of the
eccentricity beneath a wall with a horizontal
backslope and a uniform live load surcharge are as
follows, with respect to Fig. 17.
Calculate nominal retained backfill and surcharge
force resultants per unit width.
For a vertical wall, with horizontal backslope and
uniform live load surcharge, calculate the
eccentricity e as follows:
…(4.16)
45
....(4-12)
For a sloping backfill condition:
FH = FT cosβ
Pd = γEH FH = Pd = γEH FT cosβ
Rr = γEV V1 × µ
ΣMD - ΣMR
ΣV
e =
e =
γEH - MAX F1 (H/3) + γLS F2 (H/2)
γEV-MIN V1
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b) Wall with sloping backfill
The eccentricity beneath a wall with a sloping backfill and no surcharges is calculated as follows, with respect
to Fig. 17.
Calculate e with factored loads. For a wall with a sloping backfill, the eccentricity is equal to:
c) Eccentricity check criteria
e is considered acceptable if the calculated location of the resultant vertical forces (based on factored loads)
is within the one-fourth of base width for soil foundations (that is, emax ≤ L/4) and three-eighth of the base
width for rock foundations (that is, emax ≤ 3/8 L). Therefore, for each strength limit load group, e must be less
than emax. If e is greater, then a longer length of reinforcement is required.
IS 18591 : 2024
46
γEH-MAX FT cosβ (h/3) - γEH-MAX FT sinβ - γEV-MIN V2
γEV-MIN V1 + γEV-MIN V2 + γEH-MAX FT sinβ
( )
L
2
( )
L
6
e = ...(4.17)
R = Resultant of Vertical Forces
FIG. 17 CALCULATION OF ECCENTRICITY AND VERTICAL STRESS FOR BEARING CHECK, FOR HORIZONTAL
BACKSLOPE WITH TRAFFIC SURCHARGE CONDITION
qT = Live Load (Traffic Surcharge)
H
qT qT
H
2
H
3
L
B
CLE
H
F2 = qTHKab
F1 =
1
2
γbH2
Kab
V1 = γrHL
L-2e
e C
R
σv
Kab qT
Reinforced Soil Zone
Φ. γr
Retained backfill
Φ γb
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FIG. 18 CALCULATION OF ECCENTRICITY AND VERTICAL STRESS FOR BEARING CHECK, FOR SLOPING BACKSLOPE
CONDITION
34.12.3 Evaluate Bearing Capacity
34.12.3.1 Bearing calculations require both a
strength limit state and a service limit state
calculation. The strength limit calculations check
that the factored bearing pressure is less than the
factored bearing resistance. Service limit
calculations are used to compute nominal bearing
pressure for use in settlement calculations. The
weight and width of the wall facing are typically
neglected in the calculations. The bearing check
applies live load above both the reinforced zone
and the retained backfill, as shown in Fig. 11.
General Shear* — To prevent bearing failure on a
uniform foundation soil, the factored vertical
pressure at the base of the wall, as calculated with
the uniform Meyerhof-type distribution, does not
exceed the factored bearing resistance of the
foundation soil:
…..(4-18)
The uniform vertical pressure is calculated as:
…..(4-19)
where
ΣV = summation of vertical forces;
L = width of foundation, equal to reinforcement
length L at base; and
eB = eccentricity for bearing calculation (not
equal to eccentricity check e).
The eccentricity in equation (4-19) is different from
that of the eccentricity in limiting eccentricity
criteria check because different load factors
(maximum in place of minimum) are considered.
Also note that bearing check applies the live load
above both the reinforced zone and the retained
backfill.
34.12.3.2 Calculation steps for reinforced soil wall
with either a horizontal backslope or uniform live
load surcharge and for sloping backfill are as
follows:
a) Calculate the eccentricity, eB, of the
resulting force with factored loads. For a
wall with horizontal backslope and uniform
live load surcharge centered about the
reinforced zone, the eccentricity is equal to:
(4-20)
Where, terms mentioned in the equation were
previously defined.
47
qr ≥ quniform
σv or quniform =
∑V
L - 2eB
γEH-MAX F1 (H/3) + γLS F2 (H/2)
γEV-MAX V1 + γLS (qT)L
eB =

H
h
L/6
ℎ
3

Retained backfill
L
FT =
1
2
γbh2
Kab
L-2e
e
σv
C
R
ΦĀγb
Reinforced Soil Zone
ΦĀγr
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Note that when checking the various load factors,
and load combinations the value of eB will vary.
Also note that when the calculated value of
eccentricity, eB, is negative, a value of 0 should be
carried forward in the design stress equation, that is,
set L’ = L.
b) Calculate the factored vertical stress σV-F at
the base assuming Meyerhof-type
distribution. For a horizontal backslope and
uniform live load surcharge, the factored
bearing pressure is:
(4-21)
For a wall with sloping backfill the factored bearing
stress is:
(4-22)
Note that (L-2eB) is set equal to L when the value of
eccentricity is negative. A negative value of
eccentricity may be found for some extreme
geometries, for example, a wall section with very
long reinforcement and a steep, infinite backslope.
Note that while checking the various load factors
and load combinations the value of eccentricity, eB,
will vary and a critical value must be determined by
comparisons of applicable load combinations.
Equations 4-21 and 4-22 shall be extended to
include other loads and geometries for other cases.
c) The nominal bearing resistance, qn is
determined as:
(4-23)
where
d) The factored bearing pressure (qr) should
be greater than the factored bearing stress,
that is, qR ≥ qV-F;
(4-24)
where
ϕ = resistance factor, for reinforced soil walls
this factor is 0.65.
e) As indicated in step 2 and step 3, σV-F can
be decreased and qr can be increased by
lengthening the reinforcements, though
only marginally. The nominal bearing
resistance often may be increased by
additional subsurface investigation and
better definition of the foundation soil
properties. If adequate support conditions
cannot be achieved or lengthening
reinforcements significantly increases
costs, improvement of the foundation soil
may be considered.
NOTES
1 It shall be noted that the local/punching shear failure
are unlikely to happen owing to larger foundation
width ( 3.0 m) of reinforced soil walls and therefore,
it is sufficient to check general shear only. The local
shear failure need not be considered for reinforced soil
walls, except for lateral squeeze/foundation extrusion.
2 Lateral squeeze is a special case of local shear that
can occur when bearing on a weak cohesive soil layer
overlying a firm soil layer. Lateral squeeze failure
results in significant horizontal movement of the soil
under the structure. To prevent local shear of
structures bearing on weak cohesive soils it is required
that:
(4-25)
where
= unit weight of the reinforced fill, H is the
height of the wall and cut is the nominal
total stress cohesion of the foundation soil.
34.12.4 Internal Stability Analysis
Internal failure of a reinforced soil wall can occur in
three different ways:
a) Failure by elongation or breakage of the
reinforcements: The tensile forces in the
inclusions become large that the inclusions
elongate excessively or break, leading to
large movements and/or possible collapse
of the structure;
b) Failure by pullout: The tensile forces in the
reinforcements become larger than the
pullout resistance, leading to large
movements and/or possible collapse of the
structure; and
c) Internal direct sliding at reinforcement
level.
34.12.5 Geometric Characteristics of Soil
Reinforcements
Soil reinforcements can be either of two types that
is, inextensible (that is, metal strips, bars or grids) or
extensible (for example, geosynthetic/polymeric
materials such as polymeric straps, geogrids,
geotextiles). The internal stability analysis of
IS 18591 : 2024
48
γEV-MAX V1 + γLS (qT
) L
L - 2eB
σV-F =
γEV-MAX V1 + γEV-MAX V2 + γEV-MAX FT sinβ
L - 2eB
σV-F =
qn = cfd Nc + 0.5L'γfd Nγ + γ D (Nq - 1)
qr = ϕqn
γrH ≤ 3cut
γr
cfd = cohesion of the foundation soil;
𝛾fd = unit weight of the foundation soil;
Nc, Nq =
=
and Nγ
L’ = effective foundation width, equal to
L-2eB; set L’ = L if eB is negative.
bearing capacity coefficients (as per
IS 6403); and
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reinforced soil wall is primarily governed by the
nature of reinforcement that is, the design varies by
material type due to their extensibility relative to soil
at failure. The geometric characteristics required for
the two types of reinforcements for the design
calculations are as follows:
a) Metal strips, bars and grids — A layer of
steel strips, bars or grids is characterized by
the cross-sectional area, the thickness and
perimeter of the reinforcement element,
and the center-to-center horizontal distance
between elements; and
b) Geotextiles, polymeric strips and geogrid
— A layer of geosynthetic strips is
characterized by width of the strips and the
center-to-center horizontal distance
between them. The cross-sectional area is
not required, since the strength of a
geosynthetic strip is expressed by a tensile
force per unit width.
34.12.6 Coverage Ratio Calculations
Coverage ratio (Rc) is defined as the ratio of
effective width (b) of reinforcement measured from
the center to center of the outside of longitudinal
bars to the centre-to-centre horizontal spacing (Sh)
between the reinforcements.
(4-26)
FIG. 19 SOIL REINFORCEMENT COVERAGE RATIO FOR GEOGRID
FIG. 20 SOIL REINFORCEMENT COVERAGE RATIO FOR GEOSTRIP
For example — Coverage ratio of a geogrid strip of effective width equal to 240 mm with 2 connections and
2 strips in each connection for an average width of panel 2 000 mm is as below:
=
Width of Geogrid strip × No. of connectors × No. of strips per connector
Average width of panel
=
240 × 2 × 2
2 000
= 0.48
Sh
b
49
Rc = b/Sh
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34.12.7 Reinforcement Layout
For providing a consistent reinforced soil zone, the
vertical spacing of the reinforcement should not
exceed 800 mm. Following are the two practical
ways for reinforced soil walls:
a) For reinforcements such as strips, grids or
mats with segmental precast concrete
facings, the vertical spacing is maintained
constant and the reinforcement density is
increased with depth by increasing the
number and/size of the reinforcement; and
b) For continuous sheet reinforcements,
made of geotextiles or geogrids, a
common way of varying the reinforcement
density is to change the vertical spacing
because it easily accommodates spacing
variations. The range of acceptable
spacing is governed by consideration of
placement and compaction of the fill. The
reinforcement density (vertical spacing,
grade etc) can also be varied by changing
the strength especially if wrapped facing
techniques requiring a constant wrap
height are used.
34.12.8 Potential Failure Surface
The internal stability of the reinforced soil mass is
based on the failure plane considering the type of
failure surface based on the type of reinforcement.
This critical slip surface in RS wall is assumed to
coincide with the locus of the maximum tensile force
in each reinforcement layer. A bi-linear failure
surface that divides the reinforced zone in active and
resistant zones is considered in case of inextensible
reinforcement as shown in Fig. 20 while a rankine
failure surface is considered for extensible type of
reinforcements because such reinforcements can
elongate more than the soil, before failure and do not
significantly modify the shape of the soil failure
surface as shown in Fig. 21.
34.12.9 Define Unfactored Loads
The primary source of loadings for a reinforced soil
wall for internal stability calculations is the earth
pressure from the reinforced fill and any surcharge
loadings on the top of the reinforced soil zone. The
maximum tensile force is mainly related to the type
of reinforcement in the RS wall, which, in turn, is a
function of the modulus, extensibility, and density
of reinforcement. Fig. 21 shows the relationship
between the type of reinforcement and the
overburden stress. The Kr/Kab ratio for metallic type
reinforcement decreases from the top of the wall fill
to a constant value 6 m below this elevation while
in case of extensible reinforcement, the Kr/Kab ratio
is constant.
FIG. 21 LOCATION OF POTENTIAL FAILURE SURFACE FOR INTERNAL STABILITY DESIGN OF REINFORCED SOIL
WALLS FOR INEXTENSIBLE REINFORCEMENTS
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FIG. 22 LOCATION OF POTENTIAL FAILURE SURFACE FOR INTERNAL STABILITY DESIGN OF REINFORCED SOIL
WALLS FOR EXTENSIBLE REINFORCEMENTS
δ =
Angle of friction between retained backfill and reinforced soil, set equal to  (deg)
51
tan (Ψ - θ) =
- tan (θ - β) + tan (ϕ - β) [tan (ϕ - β) + cot (ϕ + θ - 90)][1+ tan (δ + 90 - θ) cot (ϕ + θ - 90)]
1+ tan (δ + 90 - θ) [tan (ϕ - β) + cot (ϕ + θ - 90)]
√
For walls with a face batter angle (θ) 10° or more from the vertical,
with δ = β
θ = wall batter angle
For wall with a broken backslope, use δ = β
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FIG. 23 VARIATION OF THE COEFFICIENT OF LATERAL STRESS RATIO (KR/KAB) WITH DEPTH IN A RS WALL
The lateral earth pressure coefficient Kr is
determined by applying a multiplier to the active
earth pressure coefficient. The active earth pressure
coefficient shall be computed using coulomb
expression as given in equation (4-1).
34.12.10 Calculate Factored Tensile Forces in
Reinforcement Layers
a) Calculate Horizontal Stress
The horizontal stress at any given depth within the
reinforced soil zone is expressed as:
σH = Kr [σv] + ∆σH
.....(4-27)
where, Kr is the coefficient of lateral earth pressure
in the reinforced soil zone and is obtained from Fig.
24. σv is the factored vertical pressure at a depth of
interest and H is the factored horizontal stress
due to pressure generated from external surcharges
if any.
The vertical pressure computed at each layer of
reinforcement shall take into account the
overturning effect for inextensible reinforcements.
Assumptions for the computation of factored
vertical pressure, σ v for internal stability analysis:
reinforced soil zone is assigned a load type
“EV” with a corresponding maximum load
factor of 1.35 which is always used to find
the critical stress;
2) Any vertical surcharge above the
reinforced soil zone that is due to soil or
considered as an equivalent soil surcharge
is assigned a load type “EV”. In this
scenario, a live load traffic surcharge that is
represented by an equivalent uniform soil
surcharge of height heq is assumed as load
type “EV”. This is in contrast to the
external stability analysis where the live
load traffic surcharge is assumed as load
type “LS” because in external stability
analysis the reinforced soil wall is assumed
to be a rigid block;
3) The unit weight of the equivalent soil
surcharge is assumed to be the same as the
unit weight of the reinforced soil zone, γr,
which is generally greater than or equal to
the unit weight of the retained backfill; and
4) Any vertical surcharge that is due to the
non-soil source is assigned a load type
“ES.” An example of such a load is the
bearing pressure under a spread footing on
top of reinforced soil zone. However, the
application of the load factor of
Kr/Kab
Kr/Kab
Vertical pressure due to the weight of the
1)
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γ P-ES = 1.50 that is assigned to load type
“ES” is a function of how the vertical
pressures are computed as follows:
i) If the vertical pressures are based on
nominal (that is, unfactored) loads,
then use γP-ES = 1.50; and
ii) If the vertical pressures were based on
factored loads, then use γP-ES = 1.00.
This is because once the loads are
factored they should not be factored
again.
It is recommended that the factored vertical pressure
be evaluated using both the above approaches and
the larger value chosen for analysis.
The supplemental factored horizontal pressure, H
could be from a variety of sources. Examples of
supplemental horizontal pressures are as follows:
1) Horizontal pressures due to the horizontal
(shear) stress at the bottom of a spread
footing on top of reinforced soil zone.
2) Horizontal pressures from deep foundation
elements extending through the reinforced
soil zone.
where,γ r is unit weight of soil in the reinforced soil
zone and γ EV-MAX is the maximum load factor for
load type “EV” The value of Kr is obtained by
assuming that: (i) variation of Kr/Kab ratio shown in
Fig. 22 starts from top of the reinforced soil zone,
and (ii) Kab is computed using coulomb’s
expression equation (4-1).
Supplemental horizontal pressures are assigned a
load type “ES” since they represent surcharges on or
within the reinforced soil zone. However, similar to
the vertical pressures due to non-soil loads, the
application of the maximum load factor of
γP-ES
= 1.50 that is assigned to load type “ES” is a
function of how the horizontal pressures are
compared as follows:
1) If the horizontal pressures are based on
nominal (that is, unfactored) loads, then use
γES-MAX = 1.50.
2) If the horizontal pressures were based on
factored loads, then use γP-ES = 1.00. This is
because once the loads are factored they
should not be factored again.
As with vertical pressure, it is recommended that the
factored horizontal pressure be evaluated using both
the above approaches and the larger value chosen for
analysis.
Following are the equations for horizontal stress
calculation for four different RS wall configurations:
Example 1:
Reinforced soil wall with level backfill and no
surcharge: The horizontal stress at any given
depth z below the top of the reinforced soil zone
is given as follows:
….(4-28)
Example 2:
Reinforced soil wall with sloping backfill:
Example of this configuration is shown in Fig. 13.
As shown in Fig. 23, the sloping surcharge is
approximated by an equivalent uniform soil
surcharge of height, Seq. The horizontal stress at any
depth z below the top of the reinforced soil zone is
as follows:
σH = Kr [γr (z + Seq) γEV-MAX] ....(4-29)
where = r is unit weight of soil in the reinforced
soil zone and EV-MAX is the maximum load factor
for load type “EV”. The value of Kr is obtained by
assuming that: (i) Variation of Kr/Kab ratio shown in
Fig. 22 starts from top of the reinforced soil zone,
and (ii) Kab is computed using coulomb’s expression
equation (4-1).
Example 3:
Reinforced soil wall with level backfill and live
load surcharge: this configuration is commonly
used for grade-separator roadways.
ro
The live load is assumed as an equivalent uniform
soil surcharge of height, heq (equal to 1.2 m) the
horizontal stress at any depth z below the top of the
reinforced soil zone is as follows:
σH = Kr [γr (z + heq) γEV-MAX] ....(4-30)
The value of Kr is obtained by assuming that: (i)
Variation of Kr/Kab ratio shown in Fig. 22 starts
from top of the reinforced soil zone, and (ii) Kab is
computed using coulomb’s expression equation
(4-1).
Example 4:
Bridge abutment with a spread footing on top of
The bridge superstructure rests on a spread footing
on top of a reinforced soil wall. For development of
the equation of horizontal stress, refer to Fig. 24
and Fig. 25. The live load is assumed as an
equivalent uniform soil surcharge of height, heq, the
height of the roadway fill above the reinforced soil
IS 18591 : 2024
53
σH = Kr [(γr z) γEV-MAX]
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zone is h, and ∆σv and ∆σH increase TMAX. Then the horizontal stress at any depth z below the top of the reinforced
zone is as follows:
where, ∆σv and ∆σH are the vertical and horizontal pressures at the bottom of the spread footing. The value of γP-ES
is 1.50 if unfactored pressures are used, and is 1.00 if factored pressures are used with the final value being on larger
values of (v-footing) γP-ES and (H) γP-ES.
The value of Kr is obtained by assuming that: (i) the variation of Kr/Ka ratio shown in Fig. 22 starts from the finished
pavement grade behind the spread footing, and (ii) Ka is computed using Coulomb’s expression equation (4-1).
This configuration is discussed in more detail in Section 6 reinforced soil abutments. It is included here as an
example of a complex system of surcharges that can be used to explain the computation of horizontal stress for such
cases.
IS 18591 : 2024
54
σH = Kr [γr (z + h + heq ) γEV-MAX + (∆σv-footing) γP-ES] + (∆σH ) γP-ES
...(4.31)
σv = Seqγr
Seq = equivalent uniform height of soil
L
FIG. 24 CALCULATION OF VERTICAL STRESS FOR SLOPING BACKFILL CONDITIONS FOR INTERNAL STABILITY

σv
H
0.7H
Seq = (
1
2
) 0.7 H tanβ
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.
.
.
where
D1 = effective width of applied load at any depth, calculation shown above;
bf = width of applied load. For footings which are eccentrically loaded (that is, bridge
abutment footings), set bf equal to the equivalent footing width B’
by reducing it by 2e’
,
where e’
is the eccentricity of the footing load (that is, bf - 2e’
);
Lf
Qv
Qv
’
z1
= length of footing;
= load per unit length of strip footing;
= load on isolated rectangular footing or point load; and
= depth where effective width intersects back of wall face = 2d1 - bf.
Assume the increased vertical stress due to the surcharge load has no influence on stresses used to evaluate
internal stability if the surcharge load is located behind the reinforced soil mass. For external stability,
assume the surcharge has no influence if it is located outside the active zone behind the wall.
FIG.25 DISTRIBUTION OF STRESS FROM CONCENTRATED VERTICAL LOAD FOR INTERNAL AND EXTERNAL
STABILITY CALCULATION
55
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Fig. 26 (a) Distribution of Stress for Internal Stability Calculations
56
IS 18591 : 2024
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Fig. 26 (b) Distribution of Stress for External Stability Calculations
FIG. 26 DISTRIBUTION OF STRESSES FROM CONCENTRATED HORIZONTAL LOADS
b) Calculate maximum tension, TMAX
Maximum factored tension TMAX in each
reinforcement layer per unit width of the wall based
on the vertical spacing Sv:
The term Sv is equal to the vertical reinforcement
spacing for a layer where vertically adjacent
reinforcements are equally spaced from the layer
under construction. In this case, σH, calculated at
the level of the reinforcement, is at the center of the
contributory height. The contributory height is
defined as the midpoint between vertically adjacent
reinforcement elevations, except for the top and
bottom layers reinforcement.
For the top and bottom layers of reinforcement, Sv
is the distance from the top or bottom of the wall
respectively, to the midpoint between the first and
second layers of reinforcement. Sv distances are
illustrated in Fig. 26.
....(4-32)
57
TMAX = σH SV (in force per unit reinforcement width) SUPPLIED
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FIG. 27 REINFORCEMENT LOAD CONTRIBUTORY HEIGHT
The maximum reinforcement tension, TMAX, for the
top and bottom layers of reinforcement, and for
intermediate layers that do not have equally spaced
adjacent layers, is calculated as the product of the
contributory height and the average factored
horizontal stress acting upon that contributory
height. The average stress can be calculated based
upon the tributary trapezoidal area (that is, average
of the stress at top and at the bottom of the
contributory height) or at the midpoint of the
contributory height, as illustrated in Fig. 26.
For discrete reinforcements (metal strips, bar mats,
geogrids, polymeric straps etc). TMAX (force per
unit width) may be calculated at each level as
PTMAX-UWR in terms of force per unit width of
reinforcement, as:
.....(4-33)
where
Rc = ratio of gross width of strip, sheet, or grid
to the center-to-center horizontal spacing
between the strips, sheets or grids; for
example, Rc = 1 for full coverage
reinforcement.
For discrete reinforcements of known spacing and
segmental precast concrete facing of known panel
dimensions, TMAX (force per unit width) can
alternatively be calculated per discrete
reinforcement, PTMAX-D, per panel width, defined as:
....(4-34)
Sv4
Sv3
Sv2
Sv1
Svn = contributory height to determine reinforcement tension
where
PTMAX-D = maximum factored load in
discrete reinforcement
element;
IS 18591 : 2024
58
PTMAX-UWR =
σH Sv
Rc
PTMAX-D = σH Sv WP
Np
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34.12.11 Calculate Soil Reinforcement Resistance
The factored soil resistance is the product of the
nominal long-term strength, coverage ratio and
applicable resistance factor, ϕ. The resistance
factors for the tensile rupture of RS Wall soil
reinforcements are summarized in Table 24. The
factored tensile resistance, Tr, is equal to:
element, or per unit reinforcement width. Tal is the
nominal long-term tensile strength of the
reinforcement.
The available tensile strength of
metallic reinforcements, Tal, is calculated as
follows:
Table 24 Sacrificial Thickness to be Allowed on Each Surface Exposed to Corrosion
(Clauses 34.3.6, 34.12.1.1, 34.12.11 and 35.2.4 )
Sl No. Design Working
Life (Years)
Reinforcement
Material
Sacrificial Thickness
(mm)
Land Based
Structure
Fresh Water
Structure
(1) (2) (3) (4) (5)
i) 5 B
G
0.25
0
0.25
0
ii) 10 B
G
0.35
0
0.4
0
iii) 50 B
G
1.15
0.3
1.55
0.55
iv) 60 B
G
1.35
0.38
1.68
0.63
v) 70 G 0.45 0.7
vi) 120 G 0.75 1.0
Key
B black steel (ungalvanized)
G galvanized steel
NOTES
where
PTMAX-D = maximum factored load in
discrete reinforcement
element;
WP = width of panel; and
NP = number of discrete
reinforcements per panel
width.
….(4-35)
….(4-36)
where
b = gross width of the strip, sheet or
grid;
Fy = yield stress of steel; and
Ac = design cross section area of the
steel defined as the original cross
section area minimum corrosion
losses anticipated to occur during
the design life of the wall. Refer
Table 25 for sacrificial thickness.
1 Linear interpolation may be used for intermediate service lives.
2 These values apply to steels embedded in fills.
3 Sites of special aggressiveness are to be assessed by specific study.
Tal and Tr may be expressed in terms of strength
per unit width of the wall, per reinforcement
59
Tr = ϕ Tal
Fy Ac
b
Tal =
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The available long-term strength for polymeric
reinforcements, Tal, is calculated as follows:
...(4-37)
where
Tult = ultimate tensile strength of
reinforcement;
RF = reduction factor. The product of
all applicable reduction factors;
RFID = installation damage reduction
factor;
RFCR = creep reduction factor;
RFD = durability reduction factor; and
RFW = weathering reduction factor.
a) Ultimate tensile strength of the
reinforcement — Tult is taken as the basis
for the long term strength. It is a statistical
value generated from the mean strength of
production material less two standard
deviations sometimes referred to as the
minimum average roll value (MARV),
unless otherwise defined;
b) Installation damage reduction factor — A
reduction factor that accounts for the
damaging effects of placement and
compaction of soil or aggregate over the
geosynthetic during installation. This
factor shall be determined based on actual
installation damage test. This test shall be
carried out as per method given in
IS 17368;
c) Creep reduction factor — A reduction
factor that accounts for the effect of creep
resulting from long-term sustained tensile
load applied to the geosynthetic. Creep
testing is essentially a constant load test on
multiple product samples, loaded to various
percentages of the ultimate product load,
for periods of up to 10 000 h. Creep testing
shall be carried out by ‘conventional’ creep
testing as per IS 14739 or a combination of
stepped isothermal method (SIM) as per
IS 17365, which is an accelerated method
using stepped increases in temperature to
allow tests to be performed in a matter of
days;
d) Durability reduction factor — Reduction
factor for durability is dependent on
susceptibility of geogrid to attack by
chemicals, thermal oxidation, hydrolysis,
environmental stress cracking and
micro-organisms. Durability tests shall be
carried out as per IS 17365; and
e) Weathering reduction factor — Reduction
factor for weathering account for
reinforcement exposure prior to installation
or of permanently exposed material.
RFID, RFCR, RFD and RFW reflect the actual long term
strength losses, analogous to loss of steel strength
due to corrosion. Some strength losses occur
immediately upon installation, and others occur
throughout the design life of the reinforcement.
Much of the long-term strength loss does not begin
to occur until near the end of the reinforcement
design life. It is recommended that tal values for
specific products be determined from in-house,
agency evaluation or third-party evaluation of
independent test results.
The designer should check to make sure that the
manufacturer data are representative of the products
likely to be received at the project site (that is, the
product test data should be current, and the product
manufacturing process, polymer source etc, should
not have changed since the testing was conducted).
In all cases, the geosynthetic product line must be
re-evaluated on a periodic to assess any changes that
may affect the product and corresponding reduction
values.
IS 18591 : 2024
60
Tult
RF
Tult
RFID × RFCR× RFD × RFW
Tal = =
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Table 25 Resistance Factors for Tensile and Pull out Resistance for RSW
(Clauses 34.12.11, 34.12.13 and 34.12.15)
Sl No. Reinforcement Type and Loading Condition Resistance
Factor
(1) (2) (3) (4)
i) Metallic reinforcement and
connectors
Strip Reinforcements(1)
Static loading 0.75
Combined static/earthquake loading 1.00
Combined static/traffic barrier impact(2)
1.00
Grid Reinforcements(1,3)
Static loading 0.65
0.85
ii) Geosynthetic reinforcement and
connectors
Static loading 0.90
1.20
iii) Pullout resistance of tensile
reinforcement (metallic and
geosynthetic)
Static loading 0.90
1.00
NOTES
1 Apply to gross cross-section less sacrificial area. For sections with holes, reduce gross area in accordance with AASHTO (2007)
article 6.8.3 and apply to net section less sacrificial area.
2 Combined static/traffic barrier impact resistance factors are not presented in AASHTO.
3 Applies to grid reinforcements connected to rigid facing element, for example, a concrete panel or block. For grid reinforcements
connected to flexible facing mat or which are continuous with the facing mat, use the resistance factor for strip reinforcements.
The soil reinforcement vertical layout, factored
tensile force at each reinforcement level, and the
factored soil reinforcement resistance were defined
in the previous three steps (a, b and c). With this
information, select suitable grades (or strength)
of reinforcement, or number of discrete
reinforcements, for the defined vertical
reinforcement layout. Then with this layout check
pullout and, as applicable extreme event loadings.
Adjust the layout if/as necessary.
34.12.12 Internal Stability with Respect to Rupture
Stability with respect to breakage of the
reinforcement required that:
TMA X ≤ Tr ….(4-38)
where
TMAX = the maximum factored load in
reinforcement equation (4-32); and
Tr the factored reinforcement tensile
resistance equation (4-35).
34.12.13 Internal Stability with Respect to Pull-Out
or Adherence
The following criteria should be satisfied for safety
against pullout of reinforcement:
….(4-39)
where
TMAX = maximum reinforcement
tension;
Le = the length of embedment in the
resisting zone. Note that the
boundary between the resisting
and active zones may be
modified by concentrated
loadings;
F* = pull-out resistance factor:
a) 1.2 + log Cu at top of
structure and tanr at a
depth of 6m or below for
metallic reinforcement;
61
=
Le ≥
TMAX
F* ασV CRc
ϕ
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b) 0.7 tanr to tanr for
geogrids, geostraps and
geotextiles in the absence
of test results. If test results
are available, the F* value
shall be according to the
test results; and
c) 1.1 at top and 0.8tan r at
6 m or below with soil as
reinforced fill for
polymeric straps or
geostrips. 1.0 at top and
0.7 tan r at 6 m or below
with flyash as reinforced
fill for polymeric straps or
geostrips. It is applicable
for full height reinforced
soil walls and should be
necessarily be supported
with test results
showcasing the value of
F* at different normal
stresses.
Pullout resistance factor
shall be verified using
pullout test;
Α = scale correction factor
(generally 1.0 for metallic
reinforcement and 0.8 for
geosynthetics reinforcements
that is geogrids). For polymeric
strap, a default scale effect
correction factor of 0.8 can be
adopted for design. However,
higher scale correction factor
can be used if substantiated by
pull out test data to account for
non-linear stress reduction over
the embedded length
of reinforcements, strain
softening of compacted
reinforced fill, extensibility of
the reinforcing element and
different lengths of reinforcing
element;
σ v = nominal vertical stress at the
reinforcement level in the
resistance zone, including
distributed dead load
surcharges, neglecting traffic
loads. (see Fig. 22) for
computing v for sloping
backfills;
C = 2 for strip, grid, and sheet type
reinforcement (number of
surfaces);
Rc = coverage ratio; and
= resistance factor for soil
reinforcement pullout. Refer:
Table 25.
Each layer of reinforcement should be checked, as
pullout resistance and/or tensile loads may vary with
reinforcement layer and accordingly the required
embedment length in the resistance zone shall be
determined.
If the traffic or other live load is present, it is
recommended that TMAX be computed with the live
loads and that the pull-out resistance be computed
excluding live loads. This addresses the possibility
of the live loads being present near the front of the
wall but not above the reinforcement embedment
length. The pull-out resistance and the TMAX can be
calculated with the live load excluded if it can be
shown that the live load will be on the active and
resistant zones at the same time or on the resistant
zone alone.
If the criterion is not satisfied for all reinforcement
layers, the reinforcement length has to be increased
and/or reinforcement with a greater pull-out
resistance per unit width must be used, or the
reinforcement vertical spacing may be reduced to
decrease TMAX.
The total length of reinforcement, L, required for
internal stability is then determined from:
….(4-40)
where
La is obtained from Fig. 28 and Fig. 29 for
simple structures not supporting concentrated
external loads such as bridge abutments.
Based on Fig. 20 and Fig. 21, the
following relationships can be obtained for La:
For RS wall with extensible reinforcements, vertical
face and horizontal backfill:
where
z = depth to the reinforcement level.
For RS wall with inextensible reinforcement,
refer Fig. 20.
IS 18591 : 2024
62
L = La + Le
La = (H - z) tan (45 - ϕ'/2) ....(4-41)
ϕ
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FIG. 28 NOMINAL VERTICAL STRESS AT THE REINFORCEMENT LEVEL IN THE RESISTANT ZONE, BENEATH A
SLOPING BACKFILL
34.12.14 Check for Internal Sliding
The internal sliding shall be checked at each
reinforcement layer. The live load surcharge is not
considered over the reinforced zone as a stabilizing
force similar to external stability sliding check.
The capacity to demand ratio (CDR) for internal
sliding is the ratio of factored horizontal driving
force to the nominal vertical resisting force at a
particular reinforcement layer.
For reinforcement at jth
layer, CDR can be
estimated as the ratio of the nominal vertical
resisting force (Rr) to that of factored horizontal
driving force (Pd). The value shall be greater than
1.0 for each layer. Live load shall be excluded in
computing the vertical resistance. However, the
driving force shall include the influence due to live
load.
34.12.15 Check for Connection Strength
The connection of the reinforcements with the
facing should be designed for TMAX. The resistance
factors (ϕ) for the connectors are the same as for the
reinforcement strength and are listed in Table 25.
a) Connections to concrete panels — Metallic
reinforcements for reinforced soil walls
constructed with segmental panels are
structurally connected to the facing by
either bolting the reinforcement to a tie
strip cast in the panel or connected with a
bar connector to suitable anchorage devices
in the panels.
Polyester geogrids and geotextile should
not be cast into concrete for connections,
due to potential chemical degradation. As
per the design requirements for different
63
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connection arrangement are available for
various geosynthetics soil reinforcements.
Connection strength testing to be
conducted at accredited laboratories to
derive the ultimate connection test. The
value for ultimate connection strength
derived at laboratories, shall be always
more than 1.25 times to the TMAX.
b) Connections to Concrete Panels — The
nominal long-term connection strength,
Talc developed by frictional and/or
structural means is determined as follows:
….(4-42)
where
34.12.16 Check for Settlements, Vertical and Lateral
Wall Movements
34.12.16.1 Settlements arising due to internal
compression are normally small once compaction is
done effectively. However, the facing should be able
to cope up with the internal compression. The total
settlement can affect the functionality of the
structure in a specific manner and differential
settlements produces severe effects on the
completed structure. Therefore, it should be ensured
that the construction and post construction
settlements are within the acceptable limits. The
maximum settlement limits for various components
and conditions shall be per Table 26.
34.12.16.2 The stiffness (axial and lateral), size, and
number of bearing pads should be sized such that the
final joint opening shall be at least 15 mm ± 5 mm
unless otherwise shown on the plans.
34.12.16.3 Post construction movements occurs due
to long term settlement of foundation soil, internal
compression of reinforced fill, internal creep strain
of reinforcements and creep strain of backfill with a
high fines content. These shall generally be avoided
by limiting the internal creep strain of the
reinforcement to 1 percent.
34.12.16.4 Conventional settlement analyses should
be carried out to ensure that immediate,
consolidation, and secondary settlement are less
than the performance requirements of the project.
The settlement is evaluated under bearing pressure
computed at a Service I limit state.
34.12.16.5 Significant estimated post-construction
foundation settlements indicate that the planned top
of wall elevations need to be adjusted. This can be
accomplished by increasing the top of wall
elevations during wall design, or by providing height
adjustments within the top of wall coping, and/or by
delaying the casting of the top row of panels to the
end of erection. The required height of the top row,
would then be determined with possible further
allowance for continuing settlements. Where the
anticipated settlements and their duration, cannot be
accommodated by these measures, consideration
must be given to ground improvement techniques
such as wick drains, stone columns, dynamic
compaction, the use of lightweight fill or the
implementation of two-phased construction.
Talc = nominal long-term
reinforcement/facing
connection strength per unit
reinforcement width at a
specified confining pressure;
Tult = ultimate tensile strength of the
geosynthetic soil
reinforcement, defined as the
minimum average roll value
(MARV);
RFD = reduction factor to account for
chemical and biological
degradation; and
CRcr = long-term connection strength
reduction factor to account for
reduced ultimate strength
resulting from the connection.
IS 18591 : 2024
64
Talc =
(Tult × CRcr)
RFD
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Table 26 Maximum Settlement Limits for Various Components and Conditions
(Clause 34.12.16.1)
Sl No. Fascia Type (In Order of
Flexibility)
Longitudinal
Differential Settlement
Total Settlement
(mm)
Post Construction Settlement
After 10 Years of Operation
(mm)
(1) (2) (3) (4) (5)
i) Full height panels 1V : 500H 100
100 (see Note 5)
ii) Discrete precast concrete
panels, with initial joint
width of 20 mm, bearing
pads, L/H ≈ 1
1V : 100H 100 to 300
iii) Precast concrete segmental
blocks
1V : 200H 100 to 300
iv) Steel wire grid/mesh,
gabions
1V : 50H 100 to 300
v) Wrap around with geogrids;
geocells
1V : 20H 100 to 500
NOTES
1 The following shall be considered when high settlement is expected:
a) The fascia to be adopted should be flexible and compressible; and
b) For both panel and block fascia, slip (shear) joints shall be provided. The interval of slip joints shall be decided based on the extent of
differential settlement, and it is in the range of 25 m to 40 m.
2 When transverse differential settlements occur, the rear of the reinforced soil block would normally exceed those at the fascia end. If anticipated
differential settlements in the transverse direction are significant, the reinforcement connection with the fascia is likely to be overstressed. To reduce
(if not eliminate) such overstressing, the fill of the reinforcement zone shall be so placed, such that it slopes gently down towards the fascia end, and
the reinforcement shall be laid on the sloping surface. While this procedure is expected to reduce additional stresses at the fascia connection, it shall
require careful monitoring of surface drainage during construction to prevent rain water runoff flowing towards the fascia.
3 Two staged construction
This type of construction may be adopted where the structure is constructed on weak soils, being treated by PVDs as ground improvement technique.
The reinforced soil structure is first constructed with a soft/compressible fascia systems. The deformations shall be monitored. After consolidation
settlements have taken place, the soft facing may be covered with hard fascia with appropriate detailing to cater to further minor deformations.
4 Settlement at abutments
Differential settlement up to 100 mm may be allowed for the reinforced soil wall near an abutment. The reinforced soil end wall at the transition with
the rigid main structure system, is indent of the rigid system. The transition is through a simply supported approach slab to bridge over the two systems.
This caters to differential settlements. To avoid an uncomfortable ride across the transition at high speeds, it is recommended that the differential
settlement be limited to 100 mm.
5 Post-construction settlement may be computed as follows:
a) For non-plastic foundation soils:
1) The total post construction settlement shall be the difference between, the total settlement due to the dead load and live load, and the
total settlement due to the dead load of the structure.
b) For plastic foundation soils:
1) The total post construction settlement shall be the difference between the total settlement over 10 years plus construction time, and the
total settlement during construction time.
65
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34.13 Slope Stability Analysis
34.13.1 RS wall shall be analysed for slope stability
as per the geometry of the wall. This shall include
global stability analysis and compound stability
analysis. The evaluation of the overall stability of
RS Wall should be investigated at the Service I load
combination and using an appropriate resistance
factor. The load factor at Service I limit state is
1.0 for permanent loads.
34.13.2 The soil shear resistance factor (ϕ) is
defined as:
ϕ = 0.75; where the geotechnical
parameters are well defined, and the
slope does not support or contain a
structural element; and
ϕ = 0.65; where the geotechnical
parameters are based on limited
information, or the slope contains or
supports a structural element.
34.13.3 The stated resistance factors of 0.75 and
0.65 are (generally) approximately equivalent to the
safety factors of 1.3 and 1.5, respectively, that is:
ϕ = 0.75 ⇒ 1/0.75 ≈ 1.3 = FS ….(4-43)
ϕ = 0.65 ⇒ 1/0.65 ≈ 1.5 = FS ….(4-44)
34.13.4 Note that these resistance factors are stated
to the nearest 0.05, so as to not overstate the level of
accuracy of a resistance value. Therefore, if
assessing global stability with limit equilibrium
slope stability methods, the target safety factors are:
FS = 1.30, where the geotechnical
parameters are well defined; for
static condition and sudden draw
down condition;
FS = 1.50, where the geotechnical
parameters are based on limited
information (This shall be used only
at preliminary design stage);
FS = 1.50, where the wall/slope contains
or supports a structural element;
FS = 1.40 for other walls; and
FS = 1.10, for extreme event I (seismic
event).
34.13.5 Additional slope stability analysis to
investigate potential compound failure surfaces, that
is failure planes that pass behind or under and
through a portion of reinforced soil zone as
illustrated in Fig. 28.
34.13.6 Compound analyses should use the same
global stability resistance factors of 0.75 and 0.65.
These resistance factors are approximately
equivalent to safety factors of 1.3 and 1.5,
respectively as previously noted.
35 DESIGN FOR EXTREME EVENTS
An extreme event is one whose recurrence interval
can be thought to exceed design life. In the context
of RS walls, the extreme events with the applicable
limit state shown in parentheses that require
consideration in the design process are as follows:
a) Seismic events;
b) Vehicular impact events; and
c) Super flood events and scour.
35.1 Design of RSW for Seismic Events
During an earthquake, the retained fill exerts a
dynamic thrust, PAE on the RS wall in addition to
the static thrust. Moreover, the reinforced soil mass
is subjected to a horizontal inertia force.
a) External stability
The external stability uses a displacement-based
approach. Following is the design procedure:
1) RS wall shall be designed as per Section 4.3
for static loading;
2) The design acceleration coefficient should
be taken equal to zone factor based on the
seismic zone as given in Table 27 as per
IS 1893 (Part 1);
3) Determine the total (static + dynamic)
thrust PAE using the following method:
i) Method: Mononobe-Okabe (M-O)
formulation
…(4-45)
Where, h is the wall height along the vertical plane
within the reinforced soil mass as shown in Fig. 30
γb is the unit weight of the retained fill.
IS 18591 : 2024
66
PAE = 0.5 (KAE) γb h2
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FIG. 29 TYPICAL GEOMETRIES WHERE RS WALL COMPOUND STABILITY IS OF CONCERN: STEEP AND TALL
BACKSLOPE ON TOP OF THE WALL; TIRED WALLS; SLOPE AT THE TOP OF THE WALL AND WATER AT TOE OF THE
SLOPE
Table 27 Zone Factor
(Clauses 35.1 and 50.9.3)
Sl No.
(1) (2) (3) (4) (5)
i) II III IV V
ii) Low Moderate Severe Very severe
iii)
Seismic zone
Seismic intensity
Z 0.10 0.16 0.24 0.36
KAE is the static + dynamic earth pressure coefficient obtained from equation (4-48) as follows:
where
ξ = tan-1
(kh/1-kv) with kh = horizontal seismic coefficient and kv= vertical seismic coefficient;
Δ = angle of wall friction. Minimum of the angle of friction for the reinforced soil zone and retained
backfill;
I = the backfill slope angle = β;
ϕb = angle of internal friction for retained backfill; and
θ = slope angle of the face.
Characteristics Requirements
67
cosξ cos2 (90 - θ) cos (δ + 90 - θ + ξ)
KAE =
cos2 (ϕb - ξ - 90 + θ)
[ sin (ϕb + δ) sin (ϕb - ξ - I)
cos (δ + 90 - θ + ξ) cos (I - 90 + θ)
√ ]
2
...(4-46)
1 +
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FIG. 30 DEFINITION OF HEIGHTS FOR SEISMIC ANALYSIS
4) The horizontal and vertical seismic
coefficient (kh and kv) are applied
simultaneously and uniformly to the
reinforced and retained fill. Typically, kv is
assumed to be zero and kh is taken equal to
design acceleration coefficient.
5) PAE shall be computed using equation 4-47.
It is assumed that PAE acts at mid-height of
the vertical plane of the height and
therefore the stress due to PAE is assumed to
be distributed uniformly over the height h.
6) The horizontal inertial force, PIR of
reinforced soil mass is obtained from the
given equation:
…(4-47)
where, Am is design acceleration coefficient and is
obtained from maximum ground acceleration
coefficient (A) as follows:
….(4-48)
W is weight of the full reinforced soil mass and any
overlying permanent slopes and/or permanent
surcharges within the limits of the reinforced soil
mass. The inertial force is assumed to act at the
centroid of the mass used to determine the weight
(W).
Example of permanent surcharges are weight of
pavement layers over the reinforced soil zone.
7) Sliding stability should be checked using a
resistance factor, ϕ (=1) and the full nominal
weight of the reinforced zone and any overlying
permanent surcharges. For M-O method, the
total horizontal force is calculated as follows:
THF = Horizontal component of PAE (cos δ) + PIR +
EQ (qT) KAE H + other horizontal nominal forces
due to surcharges with load factor 1.0.
where
EQ = the load factor for live load in extreme
event I limit state and qT is the intensity
of the live load surcharge.
Sliding resistance,
RR = ΣV (m) ….(4-49)
where, m is minimum of tanϕ’r, tanϕ’fd or tanρ and
ΣV is the summation of W, PAE sinδ and permanent
nominal surcharge loads,
where I is backfill slope angle and h/2 is measures from back of wall facing
IS 18591 : 2024
68
h = H +
tan I (0.5H)
(1 - 0.5tanI)
PIR = 0.5 (Am) (W)
Am = (1.45 - A) x A
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CDRsliding = Rτ/THF 1. The design is satisfactory.
8) The limiting eccentricity and bearing
resistance should be computed following
the same procedure as discussed in static
design. Include all the applicable loads for
extreme event I and add other applicable
forces to PAE if M-O method is used; and
9) If criteria mentioned above are not met,
adjust the wall geometry and repeat the
procedure as needed.
Limitation on the use of M-O formulation
1)
2) M-O formulation is strictly applicable to
homogeneous cohesionless soils and may
not yield realistic solutions for more
complex cases involving soils which derive
shear strength from both cohesion and
friction, non-uniform backslope profiles
and complex surface loadings.
For the cases where M-O formulation leads to
unrealistic results, it is recommended that
numerical procedures using the same principles of
M-O formulation may be used such as conventional
stability programs. Generalized limit equilibrium
slope stability method may be adopted for
determining the maximum value of total thrust PAE
and follow the above-mentioned stability criteria
(that is, sliding, limiting eccentricity and bearing
resistance check) for the analysis of the RS wall.
b) Internal stability:
1) For internal stability, it is assumed that the
active wedge develops an internal dynamic
force, Pi which is expressed as follows:
….(4-50)
where, Wa is the soil weight of the active zone as
shown by the shaded area in Fig. 31 and Am is the
design acceleration coefficient. If the weight of the
facing is significant then include it in Wa
computation.
FIG. 31 SEISMIC INTERNAL STABILITY OF REINFORCED SOIL WALL
69
IS 18591 : 2024
Pi = AmWa
For backfill slope at 3H : 1V or steeper, it
may not be possible to obtain a solution for
a certain combination of variables in the
M-O formulation as the term sin(φ - ξ - I)
in equation 4.48 may become negative and
represents a limiting condition as unstable
slope condition occurs with FS = 1 wherein
the failure surface coincides with the
surface slope. As limiting condition is
approached the earth pressures based on
M-O formulation become unrealistically
large; and
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2) Reinforcements should be designed to withstand
the horizontal forces generated by the inertia
force in addition to the static forces. It is
assumed that the location and the maximum
tensile force lines do not change during seismic
loading. The inertia force distribution to the
reinforcement is obtained from the following
equation:
….(4-51)
where
Tmd = factored incremental dynamic
inertia force at layer i;
Pi = internal inertia force due to the
weight of backfill within the
active zone; and
n = number of soil reinforcement
layers within the reinforced soil
zone.
The load factor for seismic forces is equal to 1.0. The
total factored load applied to the reinforcement on a
load per unit of wall width basis is computed as
follows:
Ttotal = Tmax + Tmd …..(4-52)
where
Tmax = the factored static load applied to the
reinforcements. The reinforcements
must be designed to resist the dynamic
component of the load at any time
throughout the design life.
Internal stability with respect to rupture — For
metallic reinforcements, the resistance factors to be
used while evaluating tensile failure under combined
static and earthquake loading are as follows:
a) Strip reinforcements: 1.00; and
b) Grid reinforcements: 0.85.
Geosynthetic reinforcements do not require a creep
factor for the short duration seismic loading.
Strength loss in geosynthetics due to creep requires
long-term sustained loading. The resistance of the
reinforcement to the static component of load, Tmax,
must be handled separately from the dynamic
component of load, Tmd. The strength required to
resist Tmax must include the effects of creep, but the
strength required to resist Tmd should not include
the effects of creep.
For geosynthetic reinforcement rupture, the
components of the loads are determined as follows:
For static component:
….(4-53)
For the dynamic component:
….(4-54)
where
= resistance factor for combined
static/earthquake loading =1.20;
Srs = ultimate reinforcement tensile
resistance required to resist static
load component;
Srt = ultimate reinforcement tensile
resistance required to resist
dynamic load component;
Rc = reinforcing coverage ratio;
RF = combined strength reduction
factor to account for potential
long-term degradation due to
installation damage, creep, and
chemical aging, equal to
RFCR × RFID × RFD;
RFID = strength reduction factor to
account for installation damage to
reinforcement; and
RDD = strength reduction factor to
prevent rupture of reinforcement
due to chemical and biological
degradation.
Therefore, the required ultimate tensile resistance of
the geosynthetic reinforcement is:
…..(4-55)
Internal stability with respect to pullout or adherence
….(4-56)
where
Le = length of reinforcement in
resisting zone;
Ttotal = maximum factored reinforcement
tension;
ϕ = resistance factor for reinforcement
pull-out = 1.20;
F*
= pull-out friction factor;
α = scale effect correction factor;
IS 18591 : 2024
70
Tmd =
Pi
n
Tmax RF
ϕRc
Srs ≥
Tmd RFID RD
ϕRc
Srt ≥
Tult = Srs + Srt
Ttotal
ϕ (0.8F* ασV CRc)
Le ≥
ϕ
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σ v
= unfactored vertical stress at the
resistant zone;
C = overall reinforcement surface
area geometry factor (number of
surfaces); and
Rc = reinforcement coverage ratio.
For seismic loading conditions, pull-out resistance
factor is reduced to 80 percent of the value used for
static design, unless dynamic pull-out tests are
performed to determine F*
value.
Check for connection strength
For static component of the load:
….(4-57)
For dynamic component of the load:
….(4-58)
where
Srs = ultimate reinforcement tensile
resistance required to resist static
load component;
Tmax = applied load to reinforcement;
RFD = reduction factor to prevent
rupture of reinforcement due
to chemical or biological
degradation;
ϕ = resistance factor for combined
static/earthquake loading = 1.20;
CRcr = long-term connection strength
reduction factor to account for
reduced ultimate strength
resulting from connection;
Rc = reinforcing coverage ratio;
Srt = ultimate reinforcement tensile
resistance required to resist
dynamic load component;
Tmd = factored incremental dynamic
inertia force; and
CRR = short-term reduction factor to
account for reduced ultimate
strength resulting from
connection.
For geosynthetic connections subjected to seismic
loading, the factored long term connection strength,
ϕTac Ttotal. If the connection strength is dependent
on friction between the facing blocks and
reinforcement (for example modular block facing),
it should be reduced to 80 percent of its static value.
For mechanical connections that do not rely on a
frictional component, 0.8 multiplier is removed from
the above equations.
The required ultimate tensile resistance of the
geosynthetic reinforcement at the connection is:
….(4-59)
35.2 Vehicular Impact Events
Traffic railing impact loads are analyzed under the
extreme event II limit state. Traffic impact events
tend to affect only the internal stability of RSW.
35.2.1 Crash Barriers
The impact traffic load on barriers constructed over
the front face of walls must be designed to resist
the overturning moment by their own mass. The
wall design should ensure that the reinforcement
does not rupture or pull-out during the impact
event. This load is applied for the top two layers of
the reinforcement.
The load factors and load combination for an
extreme event II are summarized in Table 21. A
load factor, γP-EV = 1.35 is used for the static soil
load. The traffic surcharge also uses the load factor
γP-EV = 1.35 for internal stability analysis. The
static equivalent impact loads are multiplied by a
load factor, γCT = 1.00.
35.2.2 Reinforcement Rupture
It is recommended that the upper layer of soil
reinforcement shall be designed for a rupture
impact load equivalent to a static load of 33.5 kN/m
of wall and the second layer be designed with a
rupture impact load equivalent to a static load of
8.8 kN/m.
The load factor for impact is equal to 1.0. The total
factored load applied to the reinforcement on a load
per unit of wall width basis is:
where
TI = factored impact load at layer 1 or
2, respectively;
….(4-60)
....(4-61)
71
Srs ≥
Tmax RFD
0.8 ϕ (CRcr) Rc
Srt ≥
Tmd RFD
0.8 ϕ (CRR) Rc
Tult-conn = Srs + Srt
T total = Tmax + TI
Ttotal = S v Kr γr [ (Z + heq) γEV-MAX] + Ti (γCT)
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TMAX = reinforcement tension from static
earth and traffic loads; and
ti = equivalent static load for impact
load at layer i and other terms are
previously defined.
35.2.3 Reinforcement Pull-out
The pull-out resistance of the soil reinforcement to
the impact load shall be resisted over the full length
of the soil reinforcement. The traffic surcharge shall
be included in the nominal vertical stress for pull-
out resistance calculation in case of traffic impact
event. For pull-out, it is recommended that the top
layer of reinforcement be designed for a pull-out
impact load equivalent to a static load of 19.0 kN/m
of wall and the second layer for 8.8 kN/m.
35.2.4 Resistance Factors for Tensile and Pull-out
Resistance
The resistance factor is presented in Table 24 for
combined static/traffic barrier impact. A pull-out
resistance factor of 1.00 is recommended for
metallic and geosynthetic reinforcements.
35.2.5 Post and Beam Railings
Flexible post and beam barriers shall be placed at a
distance of minimum 1.0 m from the wall face,
driven 1.5 m below pavement grades and positioned
such that it does not damage the soil reinforcements.
Each of the upper two reinforcement shall be
designed for an additional horizontal load of 2.2 kN/
m of wall, for a total additional load of 4.4 kN/m.
35.3 Super Flood Events and Scour
The stability of walls and abutments in areas of
turbulent flow must be addressed in the design. Wall
design should be based on the total scour depths.
Scour should be investigated for two flood
conditions:
a) Design flood; and
b) Check flood.
This is an extreme event, and the extreme event limit
state applies. Resistance factors for this extreme
limit state may be taken as 1.0.
36 DESIGN CONSIDERATIONS FOR
COMPLEX GEOMETRIES
36.1 Superimposed Walls (2-Tier RS walls)
Reinforced soil walls with higher height shall be
given additional consideration from the viewpoint of
constructability. The wall shall be reconfigured in
superimposed walls with an offset between the
individual tiers.
The design of superimposed RS wall requires two
analyses as follows:
a) A design using simplified design rules for
calculating external stability and locating
internal failure plane for internal stability;
and
b) A slope stability analysis including both
compound and global stability analysis.
The definitions of wall heights, H1 and H2, and offset
D between walls for a 2-tier wall configuration is
shown in Fig. 32.
Depending upon the offset distance, following
are the design considerations for superimposed
RS walls:
Global stability and compound stability analysis
shall be checked considering all the walls in
different tiers together for all the cases covered
above. The upper wall is considered as a surcharge
for the lower wall in computing bearing pressure.
IS 18591 : 2024
72
a) 𝐷 ≤ (
𝐻1+𝐻2
20
), wall shall be designed as one
single wall of height H = H1 + H2, with
minimum reinforcement length L1 (for upper
tier) ≥ 0.7 H1 and L2 ≥ 0.6 H;
b) 𝐷 ≥ 𝐻2 tan(90° − ɸ r ), wall shall be
designed as independent wall with no
surcharge load of upper tier on the bottom tier
wall;
c) (
𝐻1+𝐻2
20
) 𝐷 ≤ 𝐻2 tan (45° −
ɸ r
2
), wall
shall be designed as superimposed wall.
Internal line of wall shall be shifted by D’ as
shown in Fig. 32. The surcharge load due to
upper wall on lower wall shall be 𝜎1 = 𝛾𝐻1;
and
d) 2
𝐻2 tan (45°
−
ɸ r
) 𝐷 ≤ 𝐻2tan(90° − ɸ r), wall
internal tensile force lines and the vertical
pressure shall be as indicated in Fig. 33.
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FIG. 32 MAXIMUM TENSION LINES FOR 2-TIER SUPERIMPOSED RS WALL SYSTEM
73
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FIG. 33 ADDITIONAL VERTICAL STRESS FOR INTERNAL STABILITY COMPUTATION
36.2 Trapezoidal Walls
RS wall resting on rock or any other foundation
material which will have minimal post construction
settlements that is, foundation stratum with SPT
N value greater than 50 or sound rock. The wall
shall be designed for external and internal stability
analysis. Global stability and compound stability
analysis shall also be performed.
Following are the design rules for such type of
RS wall:
a) Wall shall be represented by a rectangular
block (Lo, H) as shown in Fig. 34 having
same total height and same cross sectional
area as the stepped section for external
stability calculation;
b) Maximum tensile force line is same as in
rectangular walls as per the extensibility of
the reinforcement; and
c) Minimum base length of 0.4 H or 3 m
whichever is greater, with the difference in
length between the consecutive zones being
less than 0.15 H.
For internal stability calculations, wall is divided in
rectangular sections and for each section the
appropriate length L (L1, L2 and L3) is used for
pull-out calculations as given for simple geometry
RS walls.
36.3 Back to Back Walls
Back to back walls are those which are near to each
other such that the reinforced portion of wall come
within the active zone. As the wall comes closer,
earth pressure by the backfill on the reinforced block
decreases and at a point where the overlapping of
the reinforcement is greater than 0.3 H2 as shown
in Fig. 35 (where, H2 is the height of the shorter
wall) the earth pressure becomes zero. For
situation, when the wall is at a distance such that
D ≥ H1tan (45° - ϕ/2) as shown in Fig. 36, where
there is no interference of active wedge with the
reinforced volume, the walls will behave
independently and stability shall be obtained
accordingly.
In between the immediate geometries as discussed
above, the earth pressure shall be linearly
interpolated for analysing sliding and overturning.
37 WATER FRONT REINFORCED SOIL
WALL STRUCTURES
In addition to conventional retaining wall and bridge
abutment applications, RS walls have also been used
successfully to retain earth in waterfront locations.
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By virtue of their location adjacent to streams,
canals, rivers, lakes, coastal and other water bodies,
waterfront structures could potentially be subject to
partial inundation and drawdown cycles. The design
high flood level (HFL) in special cases discussed
subsequently shall be considered based on
a 100 years return period. Lesser return periods
may be considered based on the criticality of the
application and/or based on recommendation by the
concerned authorities-in-charge. In such conditions,
the submerged unit weight of soil below the high
flood level shall be used in internal and external
stability calculations.
FIG. 34 DIMENSIONING OF RS WALL WITH UNEVEN REINFORCEMENT LENGTHS
FIG. 35 OVERLAP IS 0.3 H2 AND MORE, NO EARTH PRESSURE FROM BACKFILL. H1 IS TALLER WALL AND H2 IS
SHORTER WALL
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FIG. 36 D ≥ H1tan (45°-Φ/2), INDEPENDENT WALLS
FIG. 37 TYPICAL CROSS SECTION OF WATER FRONT RS WALL
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The following special measures shall be considered
in design and construction of any water front
retaining structure:
a) In conditions where the waterfront
structure is subjected to fluctuations in
water level, the wall should be designed for
rapid drawdown conditions. The structure
shall be checked for stability by
considering a minimum drawdown of
1 000 mm. Greater values of drawdown
shall be considered in design when site
conditions dictate. Effective (submerged)
unit weights should be used in the
calculations for internal and external
stability beginning at levels just below the
equivalent surface of the pressure head
line;
b) Global stability check shall be done for all
critical load combinations;
c) Coarse aggregate shall be used as
reinforced zone fill up to the high water
level + 500 mm. The gradation of the
coarse aggregate to be used up to the high
water level shall be as per the gradation
allowed in the 600 mm wide drainage bay.
Alternatively, well graded free draining
material can also be used as fill material
with coefficient of uniformity (Cu) ≥ 5. The
soil shall be non-plastic with fines content
(75 micron passing) less than 5 percent;
d) The nonwoven geotextile behind the facing
shall be covered 100 percent of the
reinforced soil panel face area. The overlap
shall be minimum 500 mm;
e) A geotextile filter should be provided at the
interface of the coarse aggregate and
reinforced backfill above it, at the interface
of the retained backfill behind it, and at the
interface of the coarse gravel and subgrade
beneath it. The geotextile should be as per
specifications in (Section 3: Materials).
Adjoining sections of geotextile
filter/separator shall be overlapped by a
minimum of 300 mm; and
f) Scour protection measures shall be
provided at the toe to ensure long term
performance of the structure. Wherever
scour protection measures are provided, a
minimum embedment of 1 500 mm shall be
provided for all waterfront structures.
Otherwise, the embedment depth shall be
provided up to the scour depth + 1 000 mm.
The clauses related to pH/chemical properties of the
fill material/environment and galvanization
requirements for metallic reinforcements,
connections and facing elements are applicable as
mention in Section 3: Materials.
In addition to drawdown conditions, water front
structures may have subjected to other factors like
high velocity water flow, floating debris of varying
sizes, boulder impact, wave action. While this
section does not address the full range of such
factors that a water front structure may be subjected
to, it is advised that all these factors be taken into
account while proposing a system to be
implemented as water front structure.
38 GROUND IMPROVEMENT
38.1 Introduction
At sites with poor ground conditions, it may be
required to carry out ground improvement to ensure
the stability and serviceability of reinforced soil
structures.
Ground conditions which may require ground
improvement include:
a) Uncontrolled/unsuitable fills like loosely
dumped soils, debris, waste materials;
b) Organic soils;
c) Weak and compressible fine-grained soils;
d) Expansive soils;
e) Loose coarse-grained soils; and
f) Strata with cavities.
38.2 Factors to be Considered in the Selection of
Ground Improvement Method
A wide range of ground improvement methods are
available. The most suitable method for a particular
site should be chosen after a careful evaluation of all
relevant factors including:
a) Performance requirements of the
reinforced soil structure and the
constructed facilities supported by the
b) The reasons for which ground
improvement is carried out and the degree
of improvement required;
c) The nature and characteristics of the poor
strata which is to be improved;
d) The depth to which improvement is to be
carried out;
e) The depth of ground water table;
f) The total area which is to be treated;
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h) Availability of necessary materials,
equipment and expertise; and
j) Site constraints including access to the site
for heavy equipment, overhead clearance,
whether there are adjacent structures
which may be adversely affected by
impact, vibrations and excavations, etc,
problems due to noise, dust, etc,
availability of water.
38.3 Overview of Ground Improvement Methods
Guidelines on selection of ground improvement
methods are given in IS 13094. A broad overview of
different ground failure mechanisms for reinforced
soil structures, typical ground conditions wherein
failures may be expected and some possible ground
improvement methods is presented in Table 28.
This is only intended to give a preliminary idea and
may not cover all possible situations and
techniques.
Table 28 Failure Mechanism, Ground Conditions and Ground Improvement Methods
(Clause 38.3)
Sl No. Failure Mechanism Susceptible Ground
Conditions
Suitable Ground Improvement
Method
(1) (2) (3) (4)
i) Sliding Loose coarse grained soils Densification
Unsuitable fills, organic
soils, weak fine-grained
soils
Excavation and replacement
ii) Bearing capacity and
global stability
Loose coarse grained soils Densification
Foundation/basal reinforcement
Unsuitable fills, organic
soils
Weak fine-grained soils Excavation and replacement
PVDs with stage construction
Granular columns, stabilized soil
columns, piles
iii) Foundation extrusion Weak fine-grained soils Excavation and replacement
PVDs with stage construction
columns, piles
iv) Liquefaction Loose saturated sands Densification
v) Settlement Unsuitable fills, organic
soils
Loose coarse-grained soils Densification
Compressible fine-grained
soils
Excavation and replacement,
PVDs with stage construction,
columns, piles
g) Time available for construction;
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39 PANEL REINFORCEMENT DESIGN
39.1 The facing panels shall be designed in both
vertical and horizontal directions as a one-way
spanning slab that is subjected to a uniformly
distributed load (UDL) that is equivalent to the
reinforcement tension at the panel connections. The
UDL shall be calculated as per below equation:
….(4-62)
where
UDL = equivalent uniformly distributed load;
γf = partial safety factor for loads = 1.0;
Tmax = maximum tension per unit reinforcement
width; and
Sv = vertical reinforcement spacing.
39.2 For strip type of reinforcement, UDL can be
calculated based on the number of connection points
and maximum tension in each strip.
39.3 The panel reinforcement shall be designed
using “Limit State Approach” as per IS 456 using
the following load and material factors.
39.4 Material Factor (γm)
The design yield strength of steel shall be derived
using the below relation:
….(4-63)
where
fyd = design yield strength of steel;
fy = characteristic yield strength of steel; and
γm = 1.15 as per IS 456.
The design compressive strength of concrete shall be
derived using the below relation:
….(4-64)
39.5 The panel reinforcement provided shall satisfy
bending moment, shear stress and area of steel
checks in both directions (IS 456) and a safety factor
of 1.0 shall be targeted in both the checks.
39.6 It is suitable to use structural analysis and
design software programs, to calculate the bending
moment and shear stress imposed on the facing
panels.
39.7 The serviceability checks that are
recommended in concrete design codes IS 456, that
is, cracking and deflection checks are not required
for facing panel design.
SECTION 5
DESIGN OF REINFORCED SOIL SLOPES
40 GENERAL
40.1 Introduction
Reinforced soil slopes are reinforced soil structures
with a face inclination less than 70 to the horizontal.
Reinforced soil structures with face inclinations
greater than or equal to 70 to the horizontal should
be designed as walls in accordance with the methods
described in Section 4. With the introduction of
suitable geosynthetic reinforcement of appropriate
length, strength and spacing, it is possible to design
a reinforced soil slope with any face inclination up
to 70. In many situations, a reinforced soil slope
with considerably lower right-of-way requirements
and lesser volume of fill, could be a more attractive
solution than a normal unreinforced slope. Also in
many cases, a reinforced soil slope could be
considered as an alternative to conventional or
reinforced soil retaining walls.
40.2 Classification of Reinforced Soil Slopes
The inclination of the face of the reinforced soil
slope has a considerable influence on its behavior,
method of analysis and method of construction.
Based on the face inclination, reinforced soil slopes
are classified into steep slopes and shallow slopes:
a) Steep Slopes — Reinforced soil slopes with
face inclinations steeper than 45 to the
horizontal are termed steep slopes. Some
form of facing should be provided for steep
slopes to facilitate placement and
compaction of fill adjacent to the slope
face, to enable anchorage of reinforcement
where
= design compressive strength of concrete;
= characteristic compressive strength of
concrete; and
= 1.5.
79
UDL =
γf x Tmax
Sv
fyd =
fy
γm
fcud =
fcu
γm
fcu
fcud
γm
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in the active zone and to provide erosion
protection; and
b) Shallow Slopes — Reinforced soil slopes
with face inclinations less than or equal to
45 to the horizontal are termed shallow
slopes. It is usually possible to place and
compact soils to face inclinations less than
or equal to 45, without the need of any
formwork and a wrap-around detail to
anchor the reinforcement is usually not
required. Hence facings are generally not
required for shallow slopes (except in case
of poorly graded granular soils and fills of
lower quality like fine-grained soils, waste
materials etc). However short intermediate
reinforcements (secondary reinforcements)
may be required to ensure surficial stability
of the slope. Suitable erosion control
measures also should be provided.
40.3 Reinforced Soil Slopes Versus Walls
The major differences between reinforced soil
slopes and reinforced soil walls in terms of
materials, design and construction are as follows:
a) Because of the inclination of the slope, the
disturbing forces are less for a reinforced
soil slope and hence the demand for soil
reinforcement is likely to be less compared
to reinforced soil walls;
b) A rigid/hard facing is not necessary for a
reinforced soil slope in most situations and
flexible/vegetated facings may be
satisfactory;
c) In view of the significant face inclination
and use of flexible facings, some
post-construction deformations of the slope
face are acceptable and hence fills of lower
quality in comparison to walls could be used
for slopes. This may permit use of local fills
instead of more expensive imported granular
fills; and
d) Reinforced soil slopes with flexible facings
have better tolerance to differential
settlements and earthquakes.
In view of these advantages, a reinforced soil slope
could be a more attractive alternative to
conventional or reinforced soil walls in many
situations.
41 APPLICATION OF REINFORCED SOIL
SLOPES
41.1 Overview
The purpose of providing reinforcements in soil
slopes are as follows:
a) To enable the slope to be constructed with
a steeper face inclination than would be
possible without reinforcement;
b) To increase the stability of the slope for a
given slope angle compared to an
unreinforced slope of same inclination; and
c) To provide better confinement and
facilitate better compaction of the fill
adjacent to the slope face thus reducing the
tendency for surface sloughing.
The major considerations in use of reinforced soil
slopes could be one or more of the following:
a) To reduce the width of the slope so that less
land is required for construction;
b) To reduce the volume of fill material;
c) To use fills of lower quality or marginal
fills; and
d) To enable a more robust design.
The major applications of reinforced soil slopes are
in the construction of embankments and hillside fills
with steeper side slopes, reinstatement of failed
slopes and increasing the surficial stability and
achieving better compaction and stability of slope
faces.
41.2 Embankments
Embankments include highway and railway
embankments including approaches to bridges and
grade separators, canal embankments, embankment
dams, levees and dikes. Reinforced slope could be a
feasible option, where sufficient land is available to
accommodate the slope angle. In many situations, a
reinforced soil slope could be a more attractive
alternative to a conventional retaining wall or
reinforced soil wall with a back slope.
41.3 Hillside Fills
Construction of roads, railways, airports, buildings
and other facilities in hilly areas require earthwork
in cut and fill. Fill has to be placed and compacted
against the existing hill slope or benches cut into the
hillside. Construction of a stable unreinforced slope
may not be feasible or economical in many cases in
view of the large base width and/or volume of fill
materials. Reinforced soil slopes could be an
attractive solution in such cases.
41.4 Reinstatement of Failed Slopes
While reconstructing a failed slope, it is required to
increase the factor of safety to an acceptable level.
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This may be achieved by using flatter slope angles,
better quality fill, drainage etc. In many cases,
sufficient space for flattening the slope may not
available and there may be significant advantages in
reusing the slipped soil for reconstruction of the
slope. Use of geosynthetic reinforcement may allow
the reconstruction of the slope at the same slope
angle and using the same soil.
41.5 Reinforcement to Improve Compaction and
Increase Slope Face Stability
It is difficult to properly compact the fill material in
the close vicinity of the slope face. Specifications
usually call for additional width of fill to be placed
and compacted and then trimmed to achieve a
compacted slope face. As an alternative to this
practice, use of short lengths of low strength
geosynthetic reinforcement at a vertical spacing of
200 mm to 400 mm may be considered. A length of
1.2 m is usually adequate. Short lengths of relatively
low strength intermediate or secondary
reinforcements may be also used to improve
surficial stability in both reinforced and
unreinforced slopes.
42 MATERIALS
42.1 Reinforcement
Geogrids, woven geotextiles, reinforced non-woven
composite geotextiles and mechanically woven
double twisted hexagonal wire mesh made from
galvanized and polymer coated steel wire mesh may
be used as soil reinforcement for the construction of
reinforced soil slopes. The reinforcement materials
shall conform to the requirements given in 5.
42.2 Soils and Other Fills
42.2.1 Soils used as reinforced fill shall conform to
the requirements given in 26.3.2 and Table 5.
Manufactured materials like aggregates and sands
produced by crushing sound rocks and conforming
to these specifications also may be used as
reinforced fill. Pond/bottom/fly ash used as
reinforced fill shall conform to the requirements
given in 26.3.5. The reinforced fill shall extend the
free/rear end of the reinforcement by at least
300 mm.
42.2.2 Where soils behind the reinforced fill
comprise natural soils/geomaterials, the shear
strength parameters and pore-water pressures should
be carefully evaluated considering the
recommendations of Section 3.
42.3 Facings
42.4 Drainage
Granular drains, geonets, geocomposites, perforated
pipes, panel drains etc, along with suitable type of
geotextiles may be used for drainage of reinforced
soil slopes. The materials shall meet the
requirements given in 28, Table 10, Table 11 and
Table 12 and relevant provisions of 44.3 and
Section 9.
43 DESIGN
43.1 Design Philosophy
43.1.1 The main objectives of the design of a
reinforced soil slope is to satisfy the requirements of
safety, serviceability, durability, sustainability,
aesthetics and constructability at the lowest possible
life cycle cost.
43.1.2 The first requirement is to ensure an adequate
margin of safety against collapse of the slope. Limit
equilibrium methods are usually adopted for the
design of slopes. A failure surface is assumed and
the factor of safety against shear failure is calculated
using appropriate simplifying assumptions. A range
of potential slip surfaces are analysed and the slip
surface with the lowest factor of safety is located
using suitable search methods. It must be ensured
that the lowest factor of safety is not less than the
minimum prescribed factor of safety. In a large
number of cases, the problem can be considered to
be two-dimensional without a significant loss of
accuracy.
43.1.3 Limit state or load and resistance factor
approach have not extensively been used for the
analysis and design of slopes. Also, a lumped factor
of safety approach is more convenient to use with
most of the commercially available software for
slope stability analysis. In view of the current
practice, this code also adopts a two-dimensional
limit equilibrium method with a lumped factor of
safety approach for the analysis and design of
reinforced soil slopes. Where three-dimensional
effects are significant, the designer must make an
evaluation and use appropriate numerical methods
or other techniques.
43.2 Modes of Failure
43.2.1 Reinforced soil structures may fail to perform
their intended function by collapse or through loss
of serviceability through excessive deformations.
43.2.2 There are three modes of collapse for
reinforced soil slopes:
a) External, where the failure surface is
Facings for reinforced soil slopes shall meet the
relevant requirements given in 43 and Section 3.
located entirely outside the reinforced
zone;
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b) Internal, where the failure surface is
located entirely within the reinforced zone;
and
c) Compound, where the failure surface is
located partly within the reinforced zone
and partly outside the reinforced zone.
43.2.3 External modes of failure include the
following mechanisms (Fig. 38):
a) Sliding along the base;
c) Deep seated failure (global stability).
43.2.4 Internal and compound failure mode involves
the failure of the reinforcement in one or more of
the following (Fig. 39, Fig. 40 and Fig. 41):
a) Sliding along the reinforcement;
b) Rupture or tensile failure of reinforcement;
and
c) Adherence or pullout failure of
reinforcement.
(a) Sliding along base
(b) Local bearing capacity/lateral squeeze
b) Local bearing capacity (lateral squeeze)
failure at the toe; and
(c) Global stability
FIG. 38 EXTERNAL FAILURE MODES FOR REINFORCED SOIL SLOPES
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FIG 39 INTERNAL SLIDING
(a) Rupture of reinforcement (b) Pull-out of reinforcement
FIG. 40 INTERNAL FAILURE MODES — RUPTURE AND PULL-OUT OF REINFORCEMENT
(a) Rupture of reinforcement (b) Pull-out of reinforcement
FIG. 41 COMPOUND FAILURE MODES — RUPTURE AND PULL-OUT OF REINFORCEMENT
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43.2.5 The serviceability of a reinforced soil slopes may be affected through one or more of the following
(Fig. 42):
a) Excessive settlement of the foundation strata;
b) Excessive post-construction strain in the reinforcement; and
c) Excessive post-construction creep deformations of the saturated fine-grained soils or other fills.
(a) Settlement of foundation strata (b) Post construction strain in reinforcement
(c) Post construction creep strain in saturated fine-grained fills
FIG. 42 FAILURE OF REINFORCED SOIL SLOPES THROUGH EXCESSIVE DEFORMATION
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43.3 Design Criteria and Performance
Requirements
Reinforced soil slopes shall be designed to meet the
following performance requirements:
a) The minimum factors of safety prescribed
in Table 29 shall be ensured; and
b) The impact of deformations should be
evaluated adequate precautions should be
taken to ensure that the anticipated
deformations are within the acceptable
limits.
Table 29 Minimum Factor of Safety Against
Failure for Reinforced Soil Slopes
(Clause 43.3)
Sl No. Mode of Failure Minimum Factor
of Safety
Static Seismic
(1) (2) (3) (4)
i) Sliding 1.4 1.1
ii) Local bearing
failure (lateral
squeeze)
1.3 Not
applicable
iii) Global stability 1.4 1.1
iv) Internal stability 1.4 1.1
v) Compound
stability
1.1
43.4 External Stability
43.4.1 General
External modes of failure of reinforced soil slopes
include sliding along base, local bearing failure at
the toe (lateral squeeze) and global failure. All loads
acting on the reinforced soil slope including
self-weight of the soil, earth pressures, dead load and
live load surcharges, pore-water pressures, seepage
forces, external water pressures, seismic forces
should be considered in the stability analysis.
When the analysis indicates that the required
minimum factor of safety is not achieved against one
or more external modes of failure, several options
are available to increase the factor of safety:
a) Reduce slope angle;
b) Increase reinforcement length;
c) Use better quality fill;
d) Ground improvement;
e) Use light-weight fill;
f) Use high strength reinforcement or
mattress at the base; and
g) Internal drainage.
43.4.2 Sliding Along Base
The stability against sliding of reinforced slopes
along the base should be checked using a sliding
block (two-part wedge method) type of analysis
(Fig. 43). The frictional resistance provided by the
weakest layer, either the reinforced soil, the
foundation soil or the soil-reinforcement interface,
should be used in the analysis. The analysis is best
performed using appropriate software. The
reinforcement length should be sufficient to ensure
adequate factor of safety against sliding failure.
43.4.3 Local Bearing Failure at the Toe (Lateral
Squeeze)
If the reinforced soil slope is founded on a relatively
thin layer of weak saturated fine-grained soil, which
is underlain by competent strata, the weak soil may
squeeze out laterally due to the stresses imposed by
the reinforced soil structure (Fig. 44).
FIG. 43 SLIDING ALONG BASE
85
1.4
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FIG. 44 LOCAL BEARING FAILURE AT THE TOE
Where the thickness of the soft soil (Ds) is less than
Bs/2, where Bs is the horizontal projected width of
the slope face, the factor of safety against lateral
squeeze (F) should be calculated using the following
equation:
γ Ds tanβ
where
cu = undrained shear strength of soft soil;
Ds = thickness of soft soil;
γ = unit weight of fill;
H = height of slope;
β = inclination of slope face with horizontal;
and
ws = uniformly distributed surcharge load.
Where the thickness of soft soil (Ds) is greater
than Bs/2, the stability may be checked using a slope
stability approach.
43.4.4 Global Stability
Potential failure surfaces passing behind and below
the reinforced soil zone should be analysed
(Fig. 45). Both circular and non-circular slip
surfaces may be considered. Care should be taken
to identify any weak soil layers in the retained fill
or natural soils behind and/or foundation soils
below the reinforced soil zone. The failure surface
tends to pass through the weakest soil strata and
hence the shape of the failure surface is likely to be
strongly influenced by the presence of weak strata
or seams. Where the failure is likely to be
controlled by the presence of weak strata or other
geological features, it may be prudent to carry out
the analysis using both circular and non-circular
(wedge shaped) failure surfaces. Both short-term
and long-term stability should be investigated using
appropriate analysis using total stress or effective
stress shear strength parameters.
FIG. 45 GLOBAL STABILITY ANALYSIS
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2 cu
F =
4.14 cu
γ H + ws
+
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43.5 Internal Stability
43.5.1 General
43.5.1.1 Internal stability pertains to modes of
failure along surfaces completely located within the
reinforced soil zone. These include internal sliding,
rupture of reinforcement and pull-out of
reinforcement. The task of internal stability
analysis is to arrive at a reinforcement
layout : length, spacing and long-term design
strength : that ensures adequate factor of safety
against internal sliding and rupture or pull-out of
the reinforcement.
43.5.1.2 The most critical internal failure surface for
reinforced soil slopes depends on a number of
factors including slope geometry, fill characteristics,
surcharge loads, pore-pressures, reinforcement
layout etc. A large number of potential failure
surfaces, which may be circular or non-circular,
need to be analysed, to identify the most critical
failure surface. Therefore, internal stability analysis
is usually done using computer programs. For slopes
having simple geometry, loading conditions and soil
profile, chart solutions available in literature could
be used for preliminary design and also to verify the
results of computer programs. However, the
limitations of the chart solutions should be
considered when comparing the chart solutions with
those of more advanced methods.
43.5.1.3 Two types of limit equilibrium methods are
commonly used for slope stability analysis are also
used for the analysis and design of reinforced soil
slopes:
a) Method of slices; and
b) Sliding block analysis.
43.5.2 Method of Slices
43.5.2.1 The method of slices is a very widely used
method for the analysis of slopes and this technique
is extended to reinforced soil slopes by
incorporating the additional stabilizing force
contributed by the reinforcements (Fig. 46). Where
a reinforcement layer intersects the assumed failure
surface on a particular slice, the tension mobilized in
the reinforcement is considered. Circular slip
surfaces are the most widely used, although
non-circular and composite slip surfaces also could
be used.
43.5.2.2 The overall rotational equilibrium of the
sliding mass of soil is evaluated by comparing the
moments of the resisting and disturbing forces about
the centre of the circular slip surface. The factor of
safety against rotational failure (F) is calculated as
the ratio of the restoring moment to the disturbing
moment using the following equation.
where
MRS = restoring moment due to shear strength
of the soil along the slip surface;
MRR = restoring moment contributed by the
reinforcements which intersects the
failure surface; and
MD = disturbing moment due to the weight of
the sliding soil mass and any external
loads or surcharges acting on the sliding
mass.
FIG. 46 INTERNAL STABILITY ANALYSIS — METHOD OF SLICES USING CIRCULAR FAILURE SURFACE
.
87
F =
MRS + MRR
MD
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43.5.2.3 The restoring moment (MRR) contributed by
the reinforcement is calculated as:
where
Ti = maximum tensile force which can be
resisted by the reinforcement; and
yi = perpendicular distance from the centre of
rotation to the reinforcement.
43.5.2.4 The maximum tensile force in the
reinforcement is limited to the long-term design
strength of the reinforcement or the available
pull-out resistance of the reinforcement whichever is
lesser. The pull-out resistance of the reinforcement
is limited by the available effective anchorage
length (Le) beyond the failure surface.
43.5.2.5 A large number of potential failure surfaces
have to be analysed to locate the most critical failure
surface corresponding to the lowest factor of safety
and hence the analysis is carried out using computer
programmes. A systematic search to ensure that the
most critical failure surface is captured is an
important part of the analysis. An optimum
reinforcement layout to achieve the required factor
of safety is arrived at by a trial and error process.
43.5.3 Sliding Block Analysis
43.5.3.1 Sliding block analysis considers bi-planar
or tri-planar failure surfaces with the failure mass
divided into two blocks or three blocks respectively
(two-part wedge or three-part wedge) and the force
equilibrium of the sliding blocks are analysed. The
analysis considers various trial surfaces and then
considers the equilibrium of the mass of soil above
the selected surface. Failure surfaces starting from
various points on the slope face, preferably at each
point where the primary reinforcement intersects the
slope face should be analyzed. The length and
inclination of the failure surfaces are varied to
determine the most critical failure surface.
43.5.3.2 Whenever a reinforcement layer intersects
the failure surface, the tension mobilized in the
reinforcement is considered in the analysis.
Fig. 47 illustrates the salient features of the two-
part wedge method. The bi-planar failure surface
consists of two line segments inclined at 1 and 2
to the horizontal. In terms of the force equilibrium
of the two wedges, the problem is statically
determinate. By varying the length and inclination
of the two line segments, a large number of failure
surfaces are analyzed and the most critical failure
surface is located. The optimum reinforcement
layout is designed to ensure the required factor of
safety.
43.5.4 Check for Internal Sliding
Check for internal sliding should be carried out
using a sliding block analysis. A simplified form of
two part wedge method as illustrated in Fig. 48 is
usually used. The first segment of the bi-planar
failure surface starts from the front end of the
reinforcement and is horizontal and located along
the surface of the reinforcement. By varying the
length of the horizontal segment and the inclination
of the second segment, a large number of sliding
blocks are analyzed. The maximum length of the
horizontal segment is equal to the length of the
reinforcement. The tensile force mobilized in the
reinforcements which intersects the failure surface
will also contribute to the equilibrium of the wedges.
The spacing, length and tensile strength of the
reinforcements are designed to ensure the required
factor of safety against sliding.
43.6 Compound Stability
Failure surfaces passing partly through the
reinforced soil zone and partially through the
retained soil and/or foundation soils also should be
analysed (Fig. 49). Both circular and non-circular
failure surfaces may be used. The effect of the
reinforcement should be considered on that part of
the potential failure surface that intersects the
reinforcement layers. Both reinforcement rupture
and bond should be considered. The various
methods used to analyse internal stability may be
extended to analyse compound stability. The
reinforcement layout should be checked to ensure
that the required factor of safety against compound
failure mode is achieved.
FIG. 47 INTERNAL STABILITY ANALYSIS — TWO PART WEDGE METHOD
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MRR = ∑ Ti yi
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FIG. 48 CHECK FOR INTERNAL SLIDING
FIG. 49 COMPOUND STABILITY ANALYSIS USING CIRCULAR FAILURE SURFACES
43.7 Analysis and Design of Reinforced Soil
Slopes using Software
43.7.1 Analysis of the stability of reinforced soil
slopes against different modes of failure like sliding
along base, internal stability, compound stability and
global stability involves the analysis of a large
number of potential failure surfaces. Therefore,
analysis and design of reinforced soil slopes is
usually carried out using software. Internal stability,
compound stability and global stability checks may
be carried out using the method of slices usually
using circular failures surfaces. The search for the
critical failure surface should ensure that all
potential internal, compound and global failure
surfaces are analysed and the most critical surface
located. Sliding check should be carried out using
sliding block method of analysis using two-part or
three-part wedge method. Sliding along the base and
along the surface of all reinforcement layers should
be checked.
43.7.2 Design software may include programmes
specifically developed for the design of reinforced
soil slopes and general slope stability software. The
main advantage of specialized reinforced soil slope
design software is that they are relatively easy to use.
However, these have some limitations like limited
range of analysis methods, failure surfaces, limited
ability to handle pore water pressures and seepage,
limited choice of soil constitutive models etc. Where
more advanced analysis is required for more
complex problems, calculations may be done using
more advanced general slope stability software.
43.8 Serviceability
43.8.1 General
Serviceability of reinforced soil slopes could be
affected by one or more of the following:
a) Excessive settlement of the ground
supporting the reinforced soil slope;
b) Excessive post-construction creep strain in
the reinforcement; and
c) Excessive post-construction creep strain in
saturated fine-grained fills.
Reinforced soil slopes are flexible structures which
can tolerate appreciable amounts of vertical and
lateral deformations. Hence, in most situations the
deformations are not usually a concern with respect
to the design and performance of reinforced soil
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slopes. However, in cases where the reinforced soil
slopes are supporting structures or facilities which
are less tolerant to movements, the post
construction vertical and lateral deformations of
reinforced soil slopes should be limited to the
specified tolerable limits.
43.8.2 Settlement of Reinforced Soil Slopes
43.8.2.1 Reinforced soil slopes are flexible
structures and can accommodate appreciable
amount of settlement. Hence, settlement of the
foundation soils is not likely to have a significant
impact on the integrity of reinforced soil slopes in
most cases. However, when settlements are of a
large magnitude and associated with appreciable
lateral displacements, the possibility of cracking of
fill and/or additional forces being induced in the
reinforcement should be assessed.
43.8.2.2 Where the reinforced soil slope supports
pavements, railway tracks, foundations etc, the
allowable post construction settlement will be
governed by the permissible limits for total and
differential settlement for the structures supported
by the slope. It must be ensured that the total and
differential post construction settlements are within
the permissible limits applicable for the structures or
facilities supported by the reinforced soil slope.
43.8.3 Post-construction Creep Strain in the
Reinforcement
As a general rule, post-construction creep strain of
reinforcement is not a serious concern for reinforced
soil slopes in most situations. However, in situations
where the slope supports structures sensitive to
displacements, post-construction creep strain in the
reinforcement should be limited to 1 percent.
43.8.4 Post-construction Creep Strain in Saturated
Fine-grained Fills
The post construction creep strains in saturated
fine-grained soils are very difficult to calculate.
Where such soils are to be used and if post
construction creep strains are a concern,
consideration should be given to providing good
drainage and/or sealing of the reinforced zone.
Preferably, better quality fill should be used.
43.9 Seismic Design
43.9.1 Reinforced soil slopes are flexible structures
which can withstand earthquakes without
undergoing significant distress. In most cases, a
pseudo-static analysis would be sufficient to ensure
the stability and integrity of the structure during
earthquakes. In the pseudo-static method, the effect
of earthquake is represented by applying an
additional force at the centroid of the sliding mass
which is equal to the seismic coefficient multiplied
by the weight of the sliding mass. When analysing
using method of slices, an additional horizontal
force equal to Ah Wi (where Ah is the horizontal
seismic coefficient and Wi is the weight of the slice)
is applied at the centroid of each slice (Fig. 50). It is
assumed that this force has no influence on the
normal force and resisting moment, so that only the
driving moment is affected. External, internal and
compound stability analysis should be carried out
considering seismic forces. Where relevant, an
additional vertical force equal to AvWi (where Av is
the vertical seismic coefficient) is applied at the
centroid of each slice. Pseudo-static seismic analysis
can also be carried out using the sliding block
method.
FIG. 50 SEISMIC STABILITY ANALYSIS — ADDITIONAL FORCE DUE TO EARTHQUAKE
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43.9.2 Reinforced soil slopes are flexible structures
and hence a lower value of seismic coefficient is
appropriate for slopes in comparison to reinforced
soil walls. The design horizontal seismic coefficient
(Ah) for reinforced soil slopes may be taken as Z/2,
where Z is the seismic zone factor from
IS 1893 (Part 1).
43.9.3 In the case of important reinforced soil slopes
located in Seismic Zones IV and V, whose function
may be critically affected by displacements caused
by earthquakes or which are of exceptional height or
with very poor foundations, pseudo-static analysis
may be supplemented with more advanced methods
if required.
43.9.4 In the case of reinforced soil slopes founded
on submerged loose sands and non-plastic silts, with
corrected standard penetration test values N less than
15 in Seismic Zones III, IV and V, and less than
10 in Seismic Zone II, the liquefaction potential of
the foundation soils should be evaluated in
accordance with IS 1893 (Part 1). Marine clays and
sensitive clays also may undergo liquefaction or
cyclic failure. The liquefaction susceptibility of such
soils also should be assessed. The minimum factor of
safety against liquefaction should be greater than or
equal to 1.2. If the calculated factor of safety against
liquefaction is less than 1.2, suitable ground
improvement should be carried out prior to the
construction of the reinforced soil slope.
43.10 Surficial Stability
43.10.1 General
43.10.1.1 The length, spacing and grade of primary
reinforcements are decided based on stability
analysis to provide acceptable factor of safety
against external, internal and compound failure
modes. Primary reinforcements may not be
sufficient to ensure the stability of the very shallow
zone of soils close to the slope face.
43.10.1.2 The surficial soils may be prone to
localized instability between the primary
reinforcement, primarily due to the effects of
infiltration of water into the surficial soils. The
sources of water could be rainfall, discharge from
surface drains, leaking pipes etc. Infiltration could be
accelerated by the presence of cracks, root holes etc.
When infiltration rates are high, a perched water
table with seepage parallel to the slope face can
develop. Due to the combined effects of loss of
apparent cohesion due to saturation and development
of pore pressures due to seepage, there is an
appreciable reduction in the shear strength in the soil
and this can result in a significant reduction
in factor of safety against surficial slides. Surficial
failures are usually shallow with depth of failure
surface limited to about 1.2 m below the slope
surface.
43.10.1.3 Approaches to stabilization of slope
surface against surficial instability depend on the
slope angle and type of fill materials. The following
cases are considered:
a) Shallow slopes constructed using well-
graded soils;
b) Shallow slopes constructed using poorly
graded or marginal soils; and
c) Steep slopes.
43.10.2 Shallow Slopes — Well-Graded Soils
43.10.2.1 In the case of shallow slopes (slope face
angle  45) constructed using well-graded fills
(soils classified as GW, GM, GC, SW, SM, SC),
intermediate layers of secondary reinforcement are
usually sufficient to control surficial slope failures.
These intermediate layers of reinforcement also help
in achieving better compaction at the face, thus
increasing soil shear strength and resistance to
erosion.
43.10.2.2 The length, spacing and strength of
secondary reinforcement may depend on a number
of factors like type of soil, angle of slope, height of
slope, spacing of primary reinforcement etc. The
following minimum requirements should be
satisfied:
a) The ultimate tensile strength of secondary
reinforcement shall be greater than or equal
to 20 kN/m;
b) The maximum unreinforced thickness of
fill within a horizontal distance of 1.5 m
from the slope face shall be limited to
400 mm; and
c) The minimum length of secondary
reinforcement shall be 1.5 m.
43.10.2.3 These are only minimum requirements
and wherever necessary based on design needs,
performance requirements or site conditions, the
tensile strength and length of secondary
reinforcement should be increased and/or secondary
reinforcements should be provided at a closer
spacing to ensure stability of slope face.
43.10.3 Shallow Slopes — Poorly Graded Soils and
Marginal Fills
In the case of shallow slopes constructed using
poorly graded soils (soils classified as GP, GP-GM,
GP-GC, SP, SP-SM and SP-SC), non-plastic silts,
pond ash, fine-grained soils and other lower quality
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fills, slope face stability shall be ensured by
providing a suitable facing (Section 43.12).
43.10.4 Steep Slopes
For steep slopes (slope face angle 45), a facing is
required to ensure slope face stability. Commonly
used types of facing include:
a) Wrap-around with vegetation;
b) Galvanized welded steel wire mesh facing
units with stone infill;
c) Face wrap using mechanically woven
double twisted hexagonal wire mesh (made
from galvanized and polymer coated steel
wire mesh) with stone infill;
d) Geocells; and
e) Gabions.
43.11 Erosion Control
43.11.1 Erosion control measures are required for
shallow slopes without facing and for wrap-around
facings. Vegetation is the most commonly used
means of erosion protection. Suitability of
vegetation must be assessed with respect to all
relevant factors including the slope angle, type of
fill, intensity of rain fall, climate, and availability of
sufficient moisture throughout the year. When a
vegetated slope face is planned, the fill material
placed close to the slope face shall be suitable for
growth of vegetation. The effectiveness of
vegetation may be enhanced by using
bio-degradable erosion control blankets made of coir
or jute, permanent turf reinforcement mats, geocells
etc.
43.11.2 In the case of shallow slopes, where
vegetation is not feasible, some form of hard armour
may be considered. However, stability of this layer
against sliding must be ensured through proper
anchorage or veneer reinforcement techniques.
43.12 Design of Facings
43.12.1 General
43.12.1.1 The facing should be designed to protect
the slope face against erosion, shallow surficial
slides and sloughing. In the case of steep slopes, it is
also required to facilitate the placement and
compaction of fill. This function of
containment/confinement of fill during placement
and compaction is a temporary one and could be
done by temporary/removable formwork or by the
facing.
43.12.1.2 Considerations in the selection of the
appropriate type of facing and its design include
slope height and angle, type of fill material, type of
reinforcement, feasibility of vegetation, climate,
design life, possibility of submergence or exposure
to flowing water or currents, expected settlement
etc.
43.12.2 Vegetated Wrap-Around Facings
43.12.2.1 A geosynthetic wrap-around or wrapped
face is formed by extending the geosynthetic
reinforcement along the slope face and then
re-embedding it back into the fill for sufficient
length to develop adequate anchorage. The wrapped
face can protect the slope face against sloughing and
surficial instability. However, the fill needs to be
protected against surface erosion and the exposed
geosynthetic should be protected from ultraviolet
radiation. This can be achieved by establishing
vegetation on the slope face.
43.12.2.2 Steep slopes require face support during
construction, which could be provided through one
of the following:
a) Temporary removable formwork;
b) Soil-filled bags; and
c) Sacrificial welded wire mesh.
43.12.2.3 To keep the deformations of the slope,
face within acceptable limits, the spacing of primary
reinforcements should be limited to 500 mm for
wrap-around facing. The minimum anchorage
(re-embedment) length of reinforcement measured
from the slope face shall be 1.2 m.
43.12.2.4 The portion of the reinforcement which
wraps the slope face is essential for surficial stability
and hence durability of this portion of the
reinforcement positioned along the slope surface is
critical in ensuring the long-term stability of the
structure. If the reinforcement undergoes significant
degradation due to prolonged exposure to solar
radiation, fire, vandalism etc, the durability of the
structure may be compromised. Since protection of
the geosynthetic face wrap and erosion control is
ensured through vegetation, geosynthetic wrap-
around facing will be durable only if healthy and
sustained vegetation can be ensured. Where it is not
possible to ensure continuous vegetation, other type
of facing should be used,
43.12.3 Other Facings
Alternatives to wrap-around facings include
galvanized welded steel wire mesh facing units with
stone infill, face wrap using mechanically woven
double twisted hexagonal wire mesh (made from
galvanized and polymer coated steel wire mesh)
with stone infill, geocells, gabions or other suitable
type of facings.
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The following considerations apply in the design of
these facings:
a) The facing shall satisfactorily perform all
its required functions during construction
and throughout the entire design life of the
structure : it shall serve as a form work for
fill placement and compaction; it shall
ensure surficial stability of the reinforced
soil slope; and it shall protect the slope face
against erosion;
b) The facing shall be able to drain out water
so as to prevent the build-up of hydrostatic
pressures or excess pore water pressures;
c) Erosion of fill through the facing shall be
prevented; a suitable nonwoven geotextile
shall be provided between stone infill and
the reinforced fill, when required;
d) The facing shall be able to resist the applied
earth pressures without undergoing sliding,
overturning, structural failure or excessive
deformations of the facing units or its
components or elements;
e) A stable connection between the facing and
reinforcement shall be ensured by
developing sufficient frictional resistance
or through mechanical fixtures;
f) The facing shall not deform excessively;
and
g) The facing shall be durable.
43.13 Design of Drainage
43.13.1 Satisfactory drainage measures should be
provided to ensure that the fill does not become
water-logged or any pore-water pressures or
hydro-static pressures considered in design are not
exceeded. The design of drainage for reinforced soil
slopes is generally similar to that for reinforced soil
walls.
43.13.2 The risk due to water and the extent of
drainage measures required will depend on the type
of the reinforced soil structure and the severity of its
exposure to water:
a) Reinforced soil slopes which are above
ground water table and above high flood
levels: Examples include embankments in
sites not affected by floods and hill side
fills where the ground water table is
permanently below the founding level of
the reinforced soil structure. The main
source of water in these structures is
infiltration of rain water or snow melt from
the surface or from leaking pipes;
b) Hill side fills with high water table
conditions: Where the ground water table
can rise above the founding level of the
reinforced soil structures, relatively large
volumes of water may enter the reinforced
fill and design of drainage measures should
cater to this;
c) Reinforced soil slopes which are likely to
be partially submerged: Reinforced soil
structures located in flood-prone sites may
be subjected to partial submergence during
the floods. Design should consider the
effects of higher hydrostatic pressures and
sudden draw down; and
d) Reinforced soil slopes exposed to water
bodies: Bridge approach embankments
and reinforced soil slopes supporting
the banks of water bodies like
rivers/streams/canals/ponds/reservoirs may
be subject to periodic submergence up to
the high water level and may be impacted
by water currents. The effects of
hydrostatic pressures, seepage pressures,
scour, internal erosion and piping should be
carefully evaluated and appropriate counter
measures provided.
43.13.3 The various approaches to minimize the
effects of water include:
a) Proper surface drainage measures to
collect and dispose of the surface runoff;
b) Use of impervious barriers to minimize the
infiltration of surface water into the
c) Use of fill with sufficient permeability to
quickly remove the water entering into the
reinforced soil structure and dissipate the
excess pore water or hydrostatic pressures;
d) Provision of adequate subsurface drainage
arrangements including granular/
geosynthetic drains, perforated pipes,
panel drains, etc;
e) Designing for anticipated excess pore-
water pressures or hydrostatic pressures
including the effects of sudden drawdown;
f) Provision of appropriate granular or
geotextile filters to prevent internal
erosion and piping; and
g) Protection against scour through adequate
embedment and using scour protection
aprons.
Guidance for detailing of drainage measures is
provided in Section 9.
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43.14 Design of Ground Improvement
Ground improvement may be required in the
following situations:
a) The factor of safety against external failure
modes (sliding, bearing failure/lateral
extrusion, global stability) is not adequate,
and it is not possible to achieve the required
factor of safety by using other measures;
b) The foundation strata are susceptible to
liquefaction during earthquakes; and
c) The settlement is more than the acceptable
limit.
General guidance on ground improvement is given
in 38.
44 DETAILING
44.1 Slope Face Geometry
In the case of shallow slopes, fill is placed and
compacted to form a planar slope face at the required
angle. If slope height is large, intermediate benches
may be provided for access, for providing catch
water drains, anchorage of hard armour etc,
depending on the requirement.
In the case of steep slopes, the required slope face
inclination may be achieved by constructing the
slope face as a planar surface or as a series of vertical
and horizontal steps.
44.2 Vegetation
44.2.1 Role of Vegetation
Vegetation improves the performance of a
reinforced soil slope through a variety of functions
including:
a) Protecting the geosynthetics forming the
wrap-around face from harmful effects of
solar radiation;
b) Controlling soil erosion by absorbing the
impact of rain drops, reducing the energy
of flowing water, binding the soil particles
by the action of root reinforcement and by
serving as a barrier to downward
movement of soil;
c) Increasing the shear strength of surficial
soils through root reinforcement;
d) Reducing the weight of any potential
unstable mass of soil through
evapotranspiration; and
e) Increasing the shear strength of surficial
soils by generating suction through
evapotranspiration.
In addition, vegetation may provide ecological and
environmental benefits and results in an
aesthetically pleasing appearance of the slope face.
44.2.2 Selection of Type of Vegetation
44.2.2.1 All relevant factors and site conditions must
be carefully evaluated while selecting the type of
vegetation which is best suited for performing its
intended functions. Important considerations
include:
a) Slope geometry: steeper the slope, more
difficult it is for the soil to retain moisture
and sustain the vegetation;
b) Type of fill materials and feasibility of
using top soils close to slope face;
c) Climate and weather conditions including
rainfall, temperature and wind;
d) Whether the slope would be submerged for
long periods of time; and
e) Role of vegetation.
44.2.2.2 As far as possible native species of
vegetation should be used and invasive species
should be avoided.
44.2.2.3 Where the primary functions of vegetation
are to protect the soils from erosion and to protect
the geosynthetics from solar radiation grass type of
vegetation would be sufficient. Where surficial
stability is an important function of the vegetation,
plants, shrubs or vetiver grass with deeper, denser
and stronger root systems may be considered.
Woody vegetation can further improve the stability
of slopes. In some situations, a mix of vegetation
may give better results. It would be prudent to
consult a horticulturist or soil bioengineering
specialist while selecting the appropriate type of
vegetation.
44.2.3 Grass Type Vegetation
Grass type of vegetation is widely used for the
erosion control of both reinforced and unreinforced
fill slopes and natural slopes. Native species of grass
with sufficiently deep roots should be preferred to
the extent possible. Grass type vegetation may
be established thorough seeding, sodding or
hydro-seeding. The advantages and disadvantages of
each method must be carefully evaluated with
specific site requirements and constraints. A
bio-degradable or permanent erosion control mats
may be used to improve the performance of the grass
cover.
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44.2.4 Vetiver Grass
Vetiver is a special type of grass which offers several
advantages over ordinary type of grasses. The root
system of vetiver is deeper, denser and stronger and
gives a higher degree of erosion protection and also
provides much better surficial stability. Vetiver can
be grown in a wide range of soils and climatic
conditions and is much more tolerant to adverse
weather conditions including drought, flooding and
submergence. While vetiver offers significant
advantages, its suitability must be carefully
evaluated with respect to specific site conditions and
project requirements.
44.2.5 Woody Vegetation
Woody vegetation can be established on reinforced
soil slopes by planting living woody plant cuttings
which are capable of rooting in moist soils. The
cuttings are embedded into the fill at required
spacing during construction. Woody vegetation
offers several benefits including shading and
protection of the reinforcement, erosion control,
surficial stabilization though root reinforcement and
moisture control, ecological benefits and aesthetics.
The plant species, length of cuttings and spacing of
planting must be decided based on a careful
evaluation of all relevant factors.
44.2.6 Creeper Type Vegetation
Where the slope face is considered to be too steep
for the establishment of vegetation, and the primary
role of vegetation is to protect the geosynthetic
wrapped face from exposure to solar radiation and
aesthetic appearance, use of creeping plants that are
rooted at the bottom of the slope could be an option.
When the height of slope is more, intermediate
benches also may be considered.
44.2.7 Use of Rolled Erosion Control Products
44.2.7.1 Rolled erosion control products include a
variety of natural or synthetic manufactured
products used to control erosion and enhance
vegetation establishment and survivability. Products
include:
b) Erosion control blankets made of
bio-degradable materials like coir fibers;
and
c) Turf reinforcement mats.
44.2.7.2 Open weave coir and jute geotextiles are
woven fabrics made from coir or jute yarns with a
range of aperture sizes used to provide erosion
control and facilitate vegetation establishment.
Erosion control blankets are temporary degradable
products composed of biodegradable fibers like coir
or other materials which bound together to form a
continuous matrix to provide erosion control and
facilitate vegetation establishment.
44.2.7.3 Turf reinforcement mats are rolled erosion
control product composed of non-degradable
synthetic fibers, filaments, nets, woven wire mesh,
and/or other elements, processed into a permanent,
three-dimensional matrix of sufficient thickness.
TRMs, which may be supplemented with degradable
components, are designed to impart immediate
erosion protection, enhance vegetation
establishment and provide long-term functionality
by permanently reinforcing vegetation during and
after maturation. Turf reinforcement mats used in
applications where the erosive forces may exceed
the limits of natural unreinforced vegetation or in
areas where limited vegetation establishment is
anticipated.
44.3 Drainage
Detailing considerations for drainage arrangement
for reinforced soil slopes will be similar to those for
reinforced soil walls and guidance is given in
Section 9.
44.4 Miscellaneous Details
Design details for various components like traffic
barriers, railings, vertical and horizontal
obstructions, face penetrations etc, the
recommendations for reinforced soil walls given in
Section 10 are generally applicable for reinforced
soil slopes also.
45 CONSTRUCTION AND MAINTENANCE
The construction methodology and maintenance
practices for reinforced soil slopes are broadly
similar to those for reinforced soil walls and the
recommendations given in Section 10 are generally
applicable for reinforced soil slopes also.
a) Open weave coir and jute geotextiles;
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SECTION 6
DESIGN OF REINFORCED SOIL TRUE ABUTMENTS
46 INTRODUCTION
The usage of RS abutments (reinforced soil true
abutment and herein after called “bridge abutment”)
has gradually increased worldwide because of
simple, rapid and predictable construction process
which results in strong, durable and economical
structure. This is extensively used in many parts of
the world including in India started with four laning
of NH-6 from Dankuni to Kolaghat and Kolaghat to
Kharagpur in West Bengal and very recently in
Mumbai airport approach road. There are several
opportunities to employ this technique in upcoming
projects for faster and economical constructions.
The developments in theory, method of design and
the experience with such structures worldwide have
given confidence to the use of this technology.
47 SCOPE
The guidelines cover the design, construction and
safety aspects of RS abutments supporting structural
and traffic loads. This type of structures can be used
with advantage for carrying heavy loads and the
areas with marginal foundation soil where
abutments may otherwise require expensive deep
foundations. The guidelines in this document
include:
a) Materials and their properties that can be
used in fill and reinforcement;
b) Design methods; and
c) Construction methods.
48 TYPES OF RS ABUTMENTS, COMPONENTS
AND MATERIAL PROPERTIES
48.1 Types of RS Abutments
48.1.1 A RS abutment essentially consists of
conventional reinforced soil wall designed to
support the earth pressures behind it, as well as the
heavy, concentrated vertical and horizontal
surcharge loads imposed on it by bridge
superstructure and traffic loadings. Superstructure
loads are transmitted by a reinforced concrete beam
seat which distributes the stresses to the reinforced
soil structure underneath.
48.1.2 There are Two Types of Bridge Abutments:
a) True abutment: In a “true abutment”, the
bridge beams are directly supported on a
spread footing called ‘bank seat’ or ‘beam
seat’ which is directly rested on reinforced
soil mass; and
b) False abutment: Here the bridge beams are
rested on a RCC cap supported by a group
of piles embedded inside reinforced soil
mass transferring the load to the ground.
The load of the approach slab and any
horizontal loads on the RS mass that may
come from pile is generally ignored, if
adequate distance is maintained.
48.2 Components of RS Abutments
48.2.1 The Beam Seat
The loads from the bridge deck are transmitted by
way of a reinforced concrete distribution beam,
which rests on the reinforced soil (RS) mass and
which is proportioned to efficiently transmit the
vertical and horizontal dead and live load from the
bridge deck into the RS mass.
48.2.2 The RS Structure
The RS sub-structure is designed to support its own
mass, the earth pressures of the approach fill and the
loads transmitted from the bridge deck by way of the
distribution beams.
48.2.3 The Foundation
The standard RS structure is generally founded on
prepared ground which may be compacted fill or
may be the natural ground. Nominal embedment of
the structure is required. However, in case of pure
abutment specific care shall be taken for design of
foundation. The minimum embedment depth shall
be 1 m provided it satisfies the required settlement
criteria. (refer Table 30).
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FIG. 51 TRUE BRIDGE ABUTMENT
FIG. 52 FALSE ABUTMENT
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FIG. 53 COMPONENTS OF RS ABUTMENT
48.3 Material Properties
The main materials within RS abutments are fill,
reinforcing elements, facing and connection. (refer
Section 4 reinforced soil walls and abutments).
49 SOIL PROPERTIES
The reinforced fill soil should be gravelly sand with
no clay content. The angle of internal friction shall
be greater than or equal to 34 degrees. The fines
content shall be limited to 10 percent with no clay or
organic content. Fly ash and silty sand shall not be
used as reinforced fill material for RS abutments.
50 DESIGN PRINCIPLES
50.1 This section should be followed for RS
abutments for conventional bridge decks, with or
without expansion joints where forces from the
bridge deck are transmitted through bearings
supported on the bank seat directly into the
abutment backfill. RS abutments — both true and
mixed — should be designed according to the
standard reinforced soil design method described in
Section 4.
50.2 The configuration wherein bridge
superstructure is supported on a spread footing on
top of the reinforced soil zone may be more
economical compared to abutments supported by
deep foundations through the reinforced soil zone.
Spread footings may be considered when the
projected settlement of foundation and reinforced
soil is rapid/small or essentially complete prior to the
erection of the bridge beams. The post construction
settlement shall be limited to 50 mm after the
installation of bridge deck.
50.3 Steps in the analysis of true bridge abutments:
a) Establish project requirements including
structural loading;
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b) Establish all standard parameters required
for design of any reinforced soil structure;
c) Geometrical dimensioning of the structure;
d) Assessment of load factors and resistance
factors and summarize the same;
e) Evaluate external stability of beam seat:
1) Check sliding, bearing and limiting
eccentricity.
f) Evaluate external stability of RS wall:
1) Check sliding, bearing, limiting
eccentricity and settlement analysis.
g) Evaluate internal stability of RS wall:
1) Check for critical failure surface,
establish long term tensile resistance
of soil reinforcement and pull-out
resistance of soil reinforcement.
h) Check overall and compound stability at
serviceability limit state;
j) Design drainage and filtration; and
k) Design of foundation.
50.4 Establish Project Requirements
50.4.1 Loading from Bridge Designer
Designing the RS abutment structure is very
different from normal RS wall design. The theory
behind RS abutment has to be very well explained
to the bridge designer. Close interaction with the
bridge designer is a prerequisite to get the bridge
loading details. The typical load requirements are
described in Table 30.
Nominal (that is, unfactored) bridge reaction loads
as required for design project.
In addition to the above data, the details of bridge
dimension like the depth of the slab or girder, the
bearing dimensions, the distance between the centre
line of bearing and the edge of girder, approach slab
details etc is required. The detailed drawing shall be
prepared with all dimensions before starting the
design activity.
50.4.2 Foundation Design
RS abutment design is also critical from foundation
point of view as the design of foundation is also very
crucial and of utmost importance while considering
the SBC calculations and settlement criteria. The
post construction settlement shall be limited to
50 mm after the installation of bridge deck.
Table 30 Nominal Bridge Reaction Load as Required for the Design
(Clauses 48.2.3 and 50.4.1)
1 QLL LL due to bridge superstructure on each abutment kN/m
2 QDL DL due to bridge superstructure on each abutment kN/m *
3 V DL due to beam seat kN/m
4 FLL Horizontal inertia of bridge LL kN/m *
5 FDL Horizontal inertia of bridge DL kN/m
6 ∆PAE Dynamic (pseudo static) force acting on bridge footing kN/m
7 HLLmax maximum horizontal live load reaction (HLLmax) for braking/traction forces kN/m
8 VLLmin
minimum vertical live load reaction (VLLmin) associated with maximum
braking/traction forces
kN/m
9 HLcreep horizontal reaction for creep and shrinkage forces that occur kN/m
10 HLtemp horizontal reaction for temperature effects that occur kN/m
* The dynamic loading has to be considered for Seismic Zone as per IS 1893 (Part I), 2002.
Seismic Zone: Maximum ground acceleration ('Z' factor as per IS 1893):
NOTE — All loads shall be unfactored, calculated per running meter length. Calculated as, total load/(cross-section width-edge distance).
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50.5 Dimension of the Structure
50.5.1 Embedment Depth
The minimum embedment depth in the case of RS
abutments shall be H/10, where H is the geometric
height of the structure. However, the minimum
embedment depth shall not be less than 1.0 m in the
case of pure abutments.
50.5.2 Length of Reinforcement
In the case of bridge abutments, the minimum
reinforcement length shall be greater of
(0.6 H + 2) m or 7 m, where H is geometric height
of the structure. The length of reinforcement below
the beam seat shall extend at least 2 m beyond the
inner edge of the bank seat (refer Fig. 53).
The top two reinforcement layers of the integrated
approach behind the superstructure (behind the
beam seat) or backwall to the cut slope or retained
zone should be extended 1 m beyond the cut slope to
blend the approach way onto the roadway to create
a smooth transition as shown in Fig. 53.
50.6 Load Combinations and Load Factors
The complete list of various loads, load factors and
the load combinations which are to be considered in
design of bridge structure and associated retaining
structure (RS structure) is given in the Table 31,
Table 32 and Table 33. The applicable loads which
shall be account for the design of RSW abutment
are as follows:
a) Dead load;
b) Live load (traffic);
c) Strip load (imposed load due to bridge
superstructure);
d) Earthquake load; and
e) Hydrostatic load.
Table 31 Definition of Different Applicable Load
(Clause 50.6)
Table 32 Load Combinations and Load Factors
(Clause 50.6)
Sl No. Load Combination Limit
State
EH/ES/EV LL/LS Use one of These at a Time
EQ CT
(1) (2) (3) (4) (5) (6)
i) Strength I γp 1.75 – –
ii) Extreme event I γp γEQ 1.00 –
iii) Extreme event II and III γp 0.50 – 1.00
iv) Service I 1.00 1.00 – –
NOTES
1 γp = load factor for permanent loading. May subscript as γP-EV, γP-EH etc.
Permanent Loads
EH = Earth pressure on reinforced soil zone due to retained soil mass
ES = Crash barrier-friction slab load or w-beam load as a strip footing etc.
EV = Vertical pressure or weight of reinforced soil zone, Sloping surcharge weight, dead
load due to pavement layers etc.
Transient Loads
CT = Impact load on barriers
EQ = Earthquake load (seismic load)
LS/LL = Live load surcharge (traffic load)/vehicular live load
2 γEQ = load factor for live load applied simultaneously with seismic loads.
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Table 33 Load Factors for Permanents Load γp
(Clause 50.6)
Sl No. Type of Load Load Factor
Maximum Minimum
(1) (2) (3) (4)
i) DC: Dead load of structural components and
non-structural attachments
DC: Strength IV only
1.25
1.50
0.9
0.9
ii) DW: Dead load of wearing surface and utilities 1.5 0.65
iii) EH: Horizontal earth pressure
a) Active
b) At-Rest
1.5
1.35
0.9
0.9
iv) EV: Vertical earth pressure
a) Overall stability
b) Retaining walls and abutments
1.00
1.35
N/A
1.00
v) ES: Earth surcharge 1.5 0.75
Table 34 Applicable Load Factors
(Clause 50.7)
Sl No. Load Combination EV DC LL/LS ES EH FR
(1) (2) (3) (4) (5) (6) (7) (8)
i) Strength I, Max 1.35 1.25 1.75 1.5 1.5 1.0
ii) Strength I, Min 1.0 0.9 1.75 0.75 0.9 1.0
iii) Service I 1.0 1.0 1.0 1.0 1.0 1.0
Table 35 Applicable Resistance Factors
(Clause 50.7)
Sl No. Stability Mode Resistance Factor
(φs)
(1) (2) (3)
i) Sliding of cast in place spread footing on RS wall 0.8
ii) Sliding of RS on foundation soil 1.0
iii) Bearing resistance of RS wall 0.65
iv) Tensile resistance (for steel strips) 0.75
v) Tensile resistance (for steel strips) 0.9
vi) Pull-out resistance 0.9
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50.7 Summary of Applicable Load and Resistance Factors
As per the problem type a summary of the load and resistance factors shall be given in the Table 34 and
Table 35
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In addition to the above load factors and load cases,
it is also required to consider the critical load
conditions (temporary and permanent) that may
arise during construction, repairing and
rehabilitation of bridges (changing of bearings) or
any specific loading that may arise during the design
life of the structure.
50.8 Evaluation of External Stability of Beam
Seat
50.8.1 Dimensioning of the Beam Seat
The dimensional configuration of beam seat has to
be decided as per the bearing capacity and the
settlement criteria. The beam seat is designed as a
retaining wall. The proportioning of the bridge seat
on top of the RS wall depends on several factors
such as the deck and the girders of the bridge, the
loading conditions, the overall geometry of the
structure, and others.
50.8.2 Setback Distance (Cf)
50.8.3 Minimum Footing Width
Minimum footing width shall be 2.0 m as per
standard practice in India.
50.8.4 Clear Space
Distance between the top of the facing panel to the
bottom of the superstructure shall be maximum of
75 mm or 2 percent of the wall height (H).
50.8.5 Bearing Bed
The beam seat should be place on a bed of 750 mm
or higher thickness of well compacted clean
sand-gravel mixture (20 mm down aggregate). The
beam seat is to be placed at depth of 300 mm below
maximum anticipated frost depth, well compacted
clean sand-gravel mixture (20 mm down aggregate)
as shown in Fig. 54 below.
50.8.6 The bearing pressure applied on the
underlying soil shall be limited to 200 kPa for
serviceability condition taking into account the
effective width of the footing (B).
Overall, the bridge seat has to meet the typical
criteria for a strip footing, against sliding and
overturning failure modes considering all forces as
shown in Fig. 55.
Distance between the inner edge of the facing and
the front edge of the footing should be at least
200 mm. The distance between the center line of the
footing and the outer edge of the facing shall be at
least 1 m. If minimum footing width is 2 m as given
under the next point, the distance to center line
should be minimum 1.2 m as 200 mm is the
minimum front distance.
FIG. 54 DIMENSIONING OF BEAM SEAT
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The load from the beam seat is calculated as:
FIG. 55 LOADING FROM BEAM SEAT
where
Pv dead load (QDL) and live load
(QLL) of the bridge superstructure;
PH = lateral load due to superstructure
and other concentrated lateral
force;
V1, V2 and V3 = dead weight of beam seat;
V4 = self weight of the reinforced soil
mass; and
V0 self weight of soil behind the
beam seat.
50.8.7 Sliding Check at the Base of Spread Footing
beam seat. In the calculation of the sliding
resistance traffic loading (q) is assumed to act only
over the retained backfill and not on the reinforced
soil mass. The contribution of the traffic surcharge
load (q) and superstructure LL is ignored to
resisting horizontal force. The critical value based
on the max/min results in the extreme force effect
and govern the sliding mode of failure.
50.8.8 Bearing Resistance at the Base of Spread
Footing
Bearing pressure at the base of the beam seat must
not exceed the allowable bearing resistance. The
factored vertical pressure at the base of the beam seat
=
=
Sliding resistance shall be checked at the base of the
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is calculated according to Meyerhof-type
distribution. In the bearing resistance calculation,
the effect of the live load is considered to create the
extreme force effect and to maximize the bearing
stress. For serviceability limit state, the bearing
stress is limited to 200 kPa to limit the vertical
movement to less than approximately 12.5 mm.
50.8.9 Limiting Eccentricity at the Base Spread
Footing
Limiting eccentricity shall be checked at the base of
the beam seat. In the computation of the limiting
eccentricity contribution of the traffic loading (q)
and superstructure LL to resisting force and
moments shall be ignored. The maximum
eccentricity should be limited to B/6.
50.8.10 Evaluation of External Stability of RS Wall
The external stability check for sliding, bearing and
limiting eccentricity for RS wall needs to be checked
considering the load and resistance factors as
discussed in 34.11 and the method of design is
same as described for any standard RS wall design.
Only the additional vertical strip load and
horizontal force coming from the different load
cases of beam seat analysis shall be considered for
all external checks.
50.8.11 Sliding Resistance at the Base of the RS Wall
Sliding resistance along the base of the wall is
evaluated using the same procedure as for spread
footing on the soil. In the calculation of the sliding
resistance, effect of the live load to resisting
horizontal force is ignored that is, the sliding check
only applies the live load above the retained backfill.
Calculate the nominal components of resisting force
and the factored driving force per unit length of the
wall and check the capacity demand ratio (CDR) for
sliding.
50.8.12 Bearing Resistance at the Base of the RS
Wall
To prevent bearing capacity failure, it is required
that the vertical pressure at the base calculated by
Meyerhof distribution does not exceed allowable
bearing resistance of the foundation soil.
50.8.13 Limiting Eccentricity at the Base Spread
Footing
In the computation of the limiting eccentricity,
beneficial contribution of the live load to resisting
forces and moments shall be ignored. The critical
values from the strength limit state calculations
based on the max/min result in the extreme force
effect and govern the limiting eccentricity mode of
failure.
50.9 Internal Stability of RS Wall
50.9.1 Estimation of the Maximum Tension Line or
Critical Failure Surface
50.9.1.1 Reinforced soil walls with supporting the
bridge loads are designed as rectangular walls
considering bridge loads as surcharge loads at the
top. The design procedures for taking account of the
surcharge loads for internal stability analysis have
been outlined in reinforced soil wall section. The
similar procedure is used for the internal stability of
bridge abutment structure. It should be noted that
when a structure supports a superimposed strip load
then the influence of the strip loads may affect the
location of the line.
FIG. 56 EXTERNAL FAILURE MECHANISM OF RS WALL
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FIG. 57 LOCATION OF MAXIMUM TENSION LINE
50.9.1.2 When the surcharge slab width (footing/
beam seat width) is greater than H/3 at the top of
the reinforced soil wall, critical failure surface
(maximum tensile line) should be modified to
extend to the back edge of the spread footing as
shown in the Fig.57. This is valid for both
extensible and inextensible reinforcement. In case,
if the back edge of the footing extends beyond
H*tan (45-φ/2) from the wall face then the
maximum tension line also needs to be modified for
extensible reinforcement.
50.9.1.3 The coefficient of lateral stress (Kr) and
pullout resistance factor (F*) for inextensible and
extensible reinforcement incase of RS wall
(or RSW) can be referred from reinforced soil wall
section.
50.9.2 Calculation of Factored Tensile Load in the
Reinforcement (TMAX)
The bridge superstructure rests on a spread footing
on top of a reinforced soil wall. For development of
the equation of horizontal stress, refer to Fig. 58,
Fig. 59 and Fig. 60. The live load is assumed as an
equivalent uniform soil surcharge of height, heq,
height of the roadway fills above the reinforced soil
zone is h and ∆σV and ∆σH increase TMAX. Then the
horizontal stress at any depth Z below the top of the
reinforced zone is as follows:
...(6.1)
where
assuming a 2 V : 1 H pyramidal
distribution;
σH = increment of horizontal stress due to
the horizontal loads at the base of the
wall or layer due to overburden
pressure;
P-EV = load factor corresponding to a vertical
pressure from a dead load earth fill;
and
P-ES = load factor corresponding to the earth
surcharge loading. A value of 1.50, if
unfactored pressures are used, and
1.00, if factored pressures are used
with the final value being on larger
values of (∆σH-footing)P-ES and (∆σH)
P-ES.
Once the factored horizontal stress is computed, the
maximum tension TMAX is computed as follows:
TMAX = σH Sv …(6.2)
where
TMAX = maximum factored tensile force in the
reinforcement; and
Sv = vertical reinforcement spacing.
Because of bridge loading and retaining wall, the
stress calculation procedures inside true abutment
structure are more complex than any normal
reinforced soil structure without unusual geometries.
It is to be noted that the performance of the pure
bridge abutment depends on the connection system
and its design strength. The connection strength
must be checked for the calculated connection load.
σv-footing = increment of vertical stress due to
concentrated vertical surcharge Pv
IS 18591 : 2024
105
r
σH = Kr [γ (Z + h + heq) γEV −MAX + (∆σv−footing )γP−ES ] +
(∆σH) γP−ES
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where
D1 =
bf
=
Lf =
Qv =
Qv
’
=
z1 =
Effective width of applied load at any depth, calculation shown above
Width of applied load. For footings which are eccentrically loaded (for example, bridge
abutment footings), set bf equal to the equivalent footing width B’
by reducing it by 2e’
,
where e’
is the eccentricity of the footing load (that is, bf-2e’
).
Length of footing
Load per unit length of strip footing
Load on isolated rectangular footing or point load
Depth where effective width intersects back of wall face = 2d1-bf
Assume the increased vertical stress due to the surcharge load has no influence on stresses used to evaluate
internal stability if the surcharge load is located behind the influence zone of reinforced soil mass. For
external stability, assume the surcharge has no influence if it is located outside the active zone behind the
wall.
FIG. 58 DISTRIBUTION OF STRESS FROM CONCENTRATED VERTICAL LOAD FOR INTERNAL AND EXTERNAL STABILITY
CALCULATIONS
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FIG. 59 DISTRIBUTION OF STRESS FROM CONCENTRATED HORIZONTAL LOADS FOR INTERNAL STABILITY
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FIG. 60 DISTRIBUTION OF STRESSES FROM CONCENTRATED HORIZONTAL LOADS FOR EXTERNAL STABILITY
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RSW abutments have been built with inextensible
reinforcement during the past, but they can also be
used with extensible reinforcement. Therefore, the
maximum tensile force lines should be modified for
extensible reinforcement. All other checks should be
done as per RS wall design.
50.9.3 Reinforcement Pull-out Check
At each layer of the reinforcement stability with
respect to pull-out failure should be checked. To
ensure the stability with respect to the pull-out
failure, factored effective pull-out length should be
greater than or equal to the factored tensile load in
the reinforcement. Reinforcement pull-out check
shall be done in the same manner as given in the
reinforced wall section.
…(6.3)
where
TMAX = maximum reinforcement tension;
resisting zone. Note that the
boundary between the resisting
and active zones may be modified
by concentrated loadings;
F* = pull-out resistance factor:
a) 1.2 + log Cu at top of
structure and tan reinf. at a
depth of 6 m or below for
metallic reinforcement;
b) 0.7 tanr to tanr for
geogrids, geostraps and
geotextiles in the absence of
test results. If test results are
available, the F* value shall
be according to the test
results; and
c) 1.1 at top and 0.8 tan r at
6 m or below with soil as
reinforced fill for polymeric
straps or geostrips. 1.0 at top
and 0.7 tan r at 6 m or
below with flyash as
reinforced fill for polymeric
straps or geostrips. It is
applicable for full height
reinforced soil walls and
should be necessarily be
supported.
F1
45+r/2
cf bf
Pv2
PH2
∆σH max = 2 ∑ F /I2
I2
F2
q
bf-2e
I2 = (Cf + bf − 2e′
)tan(45 + ∅r/2)
∑ F = PH2 + F1 + F2
PH2 = lateral force due to superstructure or
other concentrated lateral loads
If footing is located completely outside active zone
behind wall, the footing load does not need to be
considered in the external stability calculations.
45+r/2
∅𝐹∗𝛼𝜎𝑉 𝐶𝑅𝐶
𝐿𝑒 ≥
𝑇MAX
1𝑚
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wth test results showcasing the
value of F* at different normal
stresses. Pull-out resistance factor
shall be verified using pull-out
test.
Α = scale correction factor (generally
1.0 for metallic reinforcement
and 0.8 for geosynthetics
reinforcements);
σV = nominal vertical stress at the
resistance zone, including
distributed dead load surcharges,
neglecting traffic loads.
(see Fig. 24) for computing σv
for sloping backfills;
reinforcement (number of
surfaces)
Rc = coverage ratio
ϕ = resistance factor for soil
reinforcement pull-out. Refer:
Table 27 of Section 4.
50.10 Overall (Global) and Compound Stability
The overall stability of the structure using rotational
or wedge analysis can be performed by various
manual or computational methods to examine the
critical failure planes passing behind and under the
reinforced zone. Additionally, slope stability
analysis should be performed to investigate the
compound failure surfaces. In compound stability,
failure planes that pass under or through the
reinforced soil mass shall be analysed. The
evaluation of the overall and compound stability
should be determined at the Service I load
combination. The minimum factor of safety to be
achieved is 1.3 in static condition and 1.1 in
seismic condition.
50.11 Wedge Stability Analysis
50.11.1 Wedge stability check can be performed for
true bridge abutment for overall and compound
analysis. Wedges are assumed to behave as rigid
bodies and may be of any size and shape. Stability
of any wedge may be maintained when friction
forces acting on the potential failure plane in
conjunction with the tensile resistance/bond of the
group of reinforcements or anchors embedded in the
fill beyond the plane is able to resist the applied
loads tending to cause movement.
50.11.2 The following factored loads shall be
considered as shown in Fig. 61:
50.11.3 The potential failure planes shall be
investigates for each of the typical points as
indicated in Fig. 62. Forces acting on each wedge
shall be resolved into two mutually perpendicular
directions. Since the forces are assumed to be in
equilibrium the two equations may be solved
simultaneously to yield the value of the tensile force
T to be resisted by reinforcing elements or anchors.
For each of the typical points the maximum value of
T should be established by analysing the forces
acting on a number of different wedges. The
maximum value of T and the corresponding value
of β’
should be used to calculate the frictional or
tensile capacity of the group of elements anchoring
the wedge.
IS 18591 : 2024
109
a) Self-weight of the fill in the wedge (W);
b) Uniformly distributed surcharge loads
(Ws);
c) Vertical strip load (SL);
d) Horizontal shear (FL);
e) Frictional and cohesive forces acting along
the potential failure plane (F); and
f) Normal reaction of the failure plane (N).
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FIG. 61 FORCES TO BE CONSIDERED FOR WEDGE STABILITY
FIG. 62 POTENTIAL FAILURE PLANES FOR WEDGE STABILITY ANALYSIS
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50.11.4 For the case of a reinforced soil wall with
simple geometry supporting uniform surcharge, the
inclination of the potential failure plane may be
taken as (45° – ϕ’f/2). However, in the more
complex general case it is not possible to give any
guidance on either the angle of the potential failure
plane which produces the maximum value of T or
on the number of points which should be checked.
These should be determined for each structure. It
may be assumed that no potential failure plane will
pass through the strip contact area representing a
bridge bank seat. When the facing consists of a
structural element formed in one piece the shear
resistance offered by the rupture of the facing may
be considered.
50.11.5 The resistance provided by an individual
layer of reinforcing elements should be taken to be
the lesser of either:
a) The frictional resistance of that part of the
layer embedded in the fill beyond the
potential failure plane or, in the case of
anchored earth, the pull-out resistance of
the part of the anchors embedded in the fill
beyond the potential failure plane (which
should be neglected when the distance
between the potential failure plane and the
start of the anchorage is less than one
metre); and
b) The tensile resistance of the layer of
elements.
50.12 Serviceability Limits
a) Post construction movements of reinforced
soil structures results from foundation
settlement, compression of fill, internal
creep strain of reinforcement, uniform or
differential settlements, creep strain of
backfill with a high fines content, etc.
These post construction movements shall
be avoided or limited to an extent following
good construction practices; and
b) The internal creep strain of the
reinforcement should be limited to the
0.5 percent for bridge abutments. This post
construction strain can be computed based
on isochronous curve adopting test
methods as per IS 17365.
51 IMPORTANT POINTS TO BE KEPT IN
MIND DURING RS ABUTMENT DESIGN
a) Keep a minimum offset from the front of
the facing to the centre line of the bridge
bearing of 1 m;
b) Keep a clear distance of 200 mm between
the back face of the facing panels and the
front edge of the footing;
c) The connection strength shall be checked at
each layer of soil reinforcement;
d) To prevent adverse stress concentration in
the reinforcement connection, the top
reinforcement layer should be located at a
depth equal to or more than 300 mm below
the footing;
e) Bearing capacity shall be checked both for
general shear failure criteria and settlement
criteria;
f) Design of the upper wall (behind the
superstructure or bank seat) shall be
designed in the same manner as the load
bearing wall (lower wall); and
g) All other checks should be done as per
RS wall design.
52 PROVISION OF CONSTRUCTION JOINT
The requirement of a construction joint is to separate
the bridge abutment from the RS wall which enables
both the systems to behave independent of each
other. As the bridge span loading is high in
magnitude, hence construction joint will help in
minimizing the settlement. Therefore, it is
recommended that construction joint shall be
provided at the junction of bridge abutment and the
RS wall.
53 BRIDGE ABUTMENT TYPICAL LAYOUT
PLAN
When the reinforced soil wall is designed as a bridge
abutment. The design of abutments may be
considered in two parts (Zone I and Zone II) as
shown in the figure below. Zone I should be
designed assuming loading from the bank seat and
the loads coming from the bridge superstructure.
The load from the bank seat should be assumed to
diffuse downwards at 2 v : 1 h so that the width of
Zone I increases linearly from bank seat level to be
0.5 H (H = geometric height of the structure)
greater in width at foundation level. The other part
that is, Zone II should be designed as a typical
reinforced soil retaining wall ignoring any
additional loading from bank seat.
54 CONSTRUCTION SEQUENCE FOR
BRIDGE ABUTMENT
a) The bridge abutment is built in several
stages and these sequences for the
construction of bridge abutment shall be
carefully considered. The sequence
includes erection of the reinforced soil
mass, followed by the construction of the
bank seat and then the installation of the
deck; and
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b) The design shall take into account the
weight of the bank seat, the dead weight of
the deck and the live loads acting on the
deck. Apart from these loads, there might
be other load cases that also have to be
taken into account such as the reinforced
soil mass carrying the weight of the bank
seat and perhaps with the soil above the
reinforced soil mass not yet up to the final
road level, which will not provide the same
restoring overburden over the soil
reinforcements for their pull-out resistance
as in the final load case. The deck is likely
to be installed before the road pavement
layers are completed and, again, the
overburden over the soil reinforcements
will be less than in the final load case. The
design should consider all the possible load
cases and state clearly on the working
drawings the arrangement and level of fill
to be in place above the reinforced soil
mass before construction of the bank seat
and also before installation of the deck.
FIG. 63 TYPICAL LAYOUT PLAN
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SECTION 7
DESIGN OF SHORED REINFORCED SOIL STRUCTURE
55 INTRODUCTION
55.1 This type of retaining wall is employed when
space is limited, or a sleek retaining wall or slope is
required. Such type of retaining structure offers a
perfect balance between cut and fill. This system is
used to stabilize steep slopes, road widening in
valleys, landslide restoration, rehabilitation, etc.
When a reinforced soil (RS) system and nailing or
ground anchor system combined together are used
on a project, there are long-term retaining benefits
provided by the shoring wall, including improving
cut slope stability and safety during construction,
reduction of lateral loads on the RS wall mass and
significant contributions to global stability. This
type of hybrid system is popularly known as
“shored RS wall” or shored reinforced soil (SRS)
system as shown in Fig. 65 below.
55.2 Shored reinforced soil structure is a
combination of in-situ soil nailed slope and
reinforced soil structure. The reinforced soil
wall/slope is constructed by connecting the
reinforcement with the soil nailed structure. This
solution is suitable when the required base width is
not available for design of any conventional
retaining structure.
55.3 In steep terrains construction of conventional
reinforced soil wall or any retaining structures may
not be always feasible due to non-availability of
required base width or sometime excavation is not
feasible particularly if traffic must be maintained
during construction. Hence, shored or hybrid
reinforced soil structure system is good alternative
in such situation.
The concept of shored reinforced soil system is to
reinforce and strengthen the unstable cut slopes by
in-situ installation of hot dip galvanized soil
nail/anchors and connecting the nails/anchors with
reinforced soil structure system to transfer the load
from build-up reinforced soil mass to in-situ soil
nails. Soil nails/anchors creates a reinforced soil
mass that is internally stable and able to retain the
ground mass within the unstable slope against active
pressure, slip circle failure and global stability. The
connection between the reinforced soil slope and
soil nail and/or ground anchors cab be
frictional/positive/mechanical in nature for full load
transfer mechanism depending on available based
width. The conventional reinforced wall or slope
design methods and system can be adopted when a
minimum base reinforcement length equivalent to
as little as 30 percent of the wall/slope height
(0.3H) for the RS wall/slope component and
provided that the RS reinforcement length is greater
than 2 m (whichever is greater).
FIG. 64 GENERIC CROSS SECTION AND DIFFERENT COMPONENTS OF AN SRS WALL SYSTEM
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56 EVALUATION OF SHORED STRUCTURE
SUITABILITY – PRE-DECISION
EVALUATION STUDIES
56.1 The pre-decision evaluation studies shall be
carried out only after completion of geotechnical site
evaluation and preliminary roadway or project
design with sufficient details. The pre-decision
evaluation studies consist of three tasks addressing
feasibility and suitability of an SRS wall system for
a given project and they are:
a) Feasibility assessment of RS wall
construction;
b) Evaluation of shoring requirements (that is,
geometry, type of shoring system); and
c) Feasibility design of the SRS wall system.
56.2 RS Wall Feasibility Assessment
56.2.1 The first task is to evaluate the feasibility of
RS wall construction for the proposed project.
Selection of the most appropriate wall type for a
given location on a project can have significant
effects on the project cost, schedule and
constructability. The same methods applied to any
project where an RS wall would be given
consideration as a potential construction method
should be used. Factors to consider in order for an
RS wall to be a viable design option include:
a) Available base width with respect to the
height of the slope or wall;
b) Economical sources of suitable fill material
available for RS wall construction;
c) Space constraints at the project location are
such that construction of an RS wall
provides an economic advantage over a
reinforced or unreinforced slope; and
d) Geotechnical foundation conditions are
suitable to support the RS structure, or
special measures for foundation
improvement can be reasonably and
economically applied.
56.2.2 After examining the above factors, a
conceptual design for the RS structure should be
completed, sufficient in detail to support evaluation
of shoring requirements and feasibility design of the
SRS wall system. This portion of the study includes
developing the performance criteria for the
structure, such as surcharge loads, design heights,
settlement tolerances, foundation bearing capacity,
required toe embedment depth, and others as
outlined in this document.
56.3 Determination of Shoring Requirements
56.3.1 Where a conventional RS wall/slope (that is,
minimum reinforcement length of 0.7 H or
trapezoidal distribution) can be constructed without
shoring the excavation, the wall can be designed and
constructed using conventional design methodology
and practices. Described in Chapter 4.
56.3.2 If space constraints dictate that construction
of the RS wall will impact traffic, several options
should be considered before implementing shoring
requirements. These options include temporary road
closures, detours, or temporary lowering of the road
grade to facilitate RS wall construction.
56.3.3 If RS wall construction is deemed viable, but
space constraints at the project location are such that
the RS wall excavation cannot be made at an
appropriate slope angle, a preliminary estimate of
the shoring requirements should be made.
56.4 Feasibility Design of SRS Wall System
56.4.1 Where shoring is required for RS wall
construction to be feasible, investigate the feasibility
of combining the two wall components into an SRS
wall system. The instances where selection of an
SRS wall system may prove viable are:
a) Fill wall constructed in steep terrain where
required bench excavation to get the
required base width of 0.7 H for traditional
RS wall/slope construction is not feasible;
b) The required base width of 0.7 H for
traditional RS wall/slope not available for
widening from any existing retaining wall
or cut slope;
c) Space unavailable to excavate for RS
reinforcement lengths due to need to
maintain traffic during wall construction;
d) Stabilization of existing slope required for
safety prior to construction of fill wall to
remediate a landslide or excessive erosion
(that is, achieve global stability); and
e) When there is scanty of fill material nearby
the proposed construction site. In such
cases, by adopting SRS wall construction,
significant amount of backfill volume can
be reduced compared to traditional
retaining structures.
56.4.2 An SRS wall system is often feasible when
global stability controls the design, or when only
a small additional roadway width is required.
Construction of an SRS wall system addresses
global stability concerns using the shoring wall
where, in addition to providing temporary
excavation support, shoring provides stability of the
earth mass behind the RS wall component.
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56.4.3 In the case where a narrow width of additional
roadway is required, existing traffic lanes may
remain open while a shoring wall is constructed to
facilitate construction of an RS wall with relatively
short reinforcement lengths (that is, SRS wall
system).
56.4.4 Once it is determined that construction of a
fill-side retaining wall requires construction of
a shoring wall, the design of the shoring structure
should consider the following questions:
a) Is shoring required for the full height of the
proposed wall, or is it possible to excavate
an unsupported soil or rock slope for a
portion of the height?
b) Can the shoring wall be constructed at a
batter or be a stepped structure?
c) What type of shoring wall is most cost
effective for the conditions at the site?
56.4.5 Because shoring is typically required for RS
wall construction in cases where insufficient
construction right-of-way prevents construction of a
temporary slope, top-down construction methods
such as soil nailing are often used.
FIG. 65 FLOW CHART-DESIGN METHODOLOGY FOR SRS WALL SYSTEMS
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57 SRS WALL DESIGN CONSIDERATIONS
The following sections provide general details and
recommendations for design of SRS walls/slopes.
57.1 Backfill Selection
The selection backfill material for shored reinforced
soil structure shall be based on the following three
situations:
a) The minimum available base width is
4 m:
1) The backfill material shall be selected
granular and free draining for use in
the reinforced fill zone of the RS
component. The careful selection of
fill is particularly critical because of
the shorter reinforcement lengths and a
potential for reduced vertical stress
due to soil arching near the shoring
wall. Select granular fill for an SRS
wall should meet the following
minimum specifications;
2) The fill should be free from organic or
other deleterious materials because the
presence of these items enhances
corrosion of steel reinforcements and
results in excessive RS wall
settlements;
3) The fill should be free draining and
have a minimum friction angle of
30 degrees, as determined by
laboratory direct shear testing. An
example specification for select
granular fill for SRS walls is presented
in Table 36. However, the frictional
strength of the specific material
gradation provided requires
verification for the available material
source. Gradation analyses should be
conducted using the IS 2720 (Part 4)
methods, and the backfill should have
a plasticity index (PI) as determined
by IS 2720 (Part 5) less than or equal
to five (5); and
4) The backfill materials shall meet the
other electro chemical properties as
described in Section 3.
Table 36 Select Granular Fill Gradation
Specification
(Clause 57.1)
Sl No. Sieve Size Percent Passing
(1) (2) (3)
i) 100 mm 100
ii) 75 mm 75 to 100
iii) 4.75 mm 20 to 70
iv) 75 m (0.075 mm) 0 to 10
b) The available based width is 4 m and
2 m
The backfill material shall be well graded
(coefficient of uniformity, Cu 5), non-
plastic, granular and free draining.
c) The available base width is 2 m
This is not covered within the scope of this
guideline. The minimum base width shall
be limited to 2 m.
58 REINFORCEMENT LENGTH
Specification of a uniform reinforcement length is
not recommended for SRS walls with battered
shoring walls. Instead, it is critical that the RS
reinforcements extend to the shoring wall interface
and/or connected to shored wall by mechanical
connection arrangement as described below. Where
adequate construction space is available (or can be
made temporarily available), it is recommended
that the upper two layers of reinforcement are
extended to a minimum length of 0.6 H or a
minimum of 1.5 m beyond the shoring wall
interface, whichever is greater, as illustrated in
Fig. 66 (A) This feature limits the potential for
tension cracks to develop at the shoring/RS
interface and resists lateral loading effects. If
extension of the upper reinforcemts is not feasible,
a positive connection between the upper two or
more reinforcements and the shoring wall is
recommended, as illiustrated in Fig. 66 (A) and
Fig. 66 (B).
Where the shoring wall is in partial height due to
available of space in top, the reinforcement lengths
in the upper part of the RS wall shall be minimum
0.7 H.
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59 INTERFACE CONNECTIONS BETWEEN
RS WALL REINFORCEMENTS AND
SHORING WALL OF SRS SYSTEM
59.1 Options for interface connections between RS
reinforcements and the shoring wall include two
general types — Mechanical and frictional.
59.2 Frictional Connection Options
(1) Wrapped-back RS reinforcements, (2) stepped
wall interface, and (3) RS reinforcements bent
upward at shoring interface. Fig. 67(A)
conceptually illustrates these frictional connection
options. Frictional connections are likely simpler to
construct. Mechanical connections require detailed
design, testing and construction oversight to ensure
that the connections are designed and constructed
appropriately. The following figures are only
indicative illustrations.
59.3 The above frictional connection arrangements
are recommended only for a minimum required
reinforcement length at base equivalent to as little
as 30 percent of the wall/slope height (0.3 H) for
the RS structure component and provided that the
RS reinforcement length is greater than 1.5 m
(whichever is greater).
FIG.66 (A) PROPOSED SRS WALL DIMENSIONING WHEN ADEQUATE SPACE IS AVAILABLE
FIG. 66 (B) ALTERNATIVE PROPOSED GEOMETRY OF RS WALL COMPONENT OF AN SRS WALL
SYSTEM WHERE LAND SPACE WILL NOT BE AVAILABLE AT THE TOP 0.3 H
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FIG. 67 (A) FRICTIONAL CONNECTION OPTIONS FOR A SRS WALL SYSTEM
FIG. 67 (B) MECHANICAL CONNECTION OPTIONS FOR AN SRS WALL SYSTEM
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59.4 Mechanical Connection Options
(1) Connect RS reinforcement layers to the nails
using direct link by mechanical means, and
(2) mechanically connect short RS reinforcements
near reinforcement levels in the shoring wall, and
extend or overlap the reinforcement “tails” into the
RS wall component during RS construction.
Fig. 67 (B) conceptually illustrates these
mechanical connection options.
59.5 In case sufficient base width is not available
( 0.3 H), all connection arrangement must be
mechanical based. The typical connection
arrangements are shown in Fig. 67 (B) for such
cases. The mechanical connection system shall be
well designed and tested for the required strength as
per detail calculations. The connection strength shall
be more than the long term design strength of the soil
reinforcement.
59.6 The mechanical connection system shall be
designed for full load transfer mechanism and
having rotational flexibility in both horizontal and
vertical plane to improve flexibility during the event
of any differential settlement. All steel components
of the connection are hot dip galvanized conforming
to requirements laid down in IS 4759, except that the
average zinc coat weight is not less than 500 gm/m2
.
The soil nail used for shored wall/slope shall be fully
threaded solid/hollow geotechnical bars which are
hot dip galvanized conforming to IS 4759
requirements, except that the average zinc coating
weight on nail surface is not less than 500 gm/m2
.
This protection measure is applicable only for
non-corrosive environment.
60 GEOMETRY OF RS/SHORING
INTERFACE
60.1 The face of the shoring wall/slope defines the
geometry of the RS/shoring interface. The shoring
system, and hence the RS/shoring interface, may be
constructed at a batter, vertically, or stepped. Where
shoring is necessary, the interface surface between
the two wall systems will generally be steep or
vertical. The wall designer should consider
designing the shoring wall with a nominal batter
(up to 10 degrees from vertical) to reduce the risk of
tension crack development. Another option, where
adequate working room is available, is construction
of a stepped interface to strengthen the system
against shear failure along the interface, illustrated
in Fig. 68 Qualitatively, offsetting the steps of the
stepped shoring wall a small amount (that is, by as
little as 0.5 m) may increase the resistance of the
SRS wall system to instability along the interface.
A slope (2 H : 1 V or flatter) may be incorporated
between shoring wall steps to nominally reduce the
shoring wall area. Whether or not a batter or stepped
geometry is employed, extension of the upper two
layers of RS reinforcements to a minimum length
of 0.6 H or direct mechanical connection with nails/
shored face is recommended to mitigate tension
crack development as shown in Fig. 66 and Fig. 68.
FIG. 68 STEPPED SHORING WALL INTERFACE
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61 DRAINAGE CONSIDERATIONS OF SRS
WALL
Because the SRS wall system is designed based on
long-term performance of both the shoring wall and
the RS wall components, wall drainage provisions
for both components are crucial. Drainage for the
shoring component should be connected to the
drainage system of the RS component or extended
through the face of the RS wall. The detail drainage
arrangement shall be considered as per Section 9.
62 DESIGN OF RS WALL COMPONENT OF
AN SRS WALL SYSTEM
62.1 Design of the RS wall component of an SRS
wall system shall consider:
a) Internal stability of the reinforced soil mass
with regard to rupture and pull-out of
reinforcing elements;
b) Internal stability of shored wall system and
mechanical connection system;
c) External stability along the RS
wall/shoring wall interface;
d) Bearing capacity and settlement of the RS
wall foundation materials; and
e) Global stability of the composite SRS wall
system.
62.2 In contrast to design of a traditional RS wall,
the resistance to sliding and overturning are not
evaluated as these are not critical for SRS wall
systems. In addition, a different method is
recommended for design of the RS reinforcements
to resist pull-out for SRS wall systems.
62.3 When an SRS wall system is selected as the
preferred alternative, the design process is iterative
between defining the geometric constraints of the
structure and analysis of stability. A number of
geometric factors for design of the SRS wall system
should be considered, including reinforcement
lengths, toe embedment, and interface geometry.
These factors are interrelated and have a combined
effect on the stability of the structure. The optimum
combination will provide the most economical
construction while meeting the necessary stability
criteria.
62.4 Potential Failure Modes
Stability analysis of an SRS wall system must
consider failure modes associated with conventional
RS walls and shoring walls, plus internal failure
modes specific to the compound nature of the SRS
wall system. Fig. 69 illustrates the various failure
modes of the composite SRS wall system.
FIG. 69 SRS WALL SYSTEM FAILURE MODES
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62.5 Factors of Safety
The recommended minimum factors of safety (FS)
for design of the SRS wall system were modified and
are provided below:
a) Global stability, FSg: 1.3;
b) Compound stability, FSc: 1.3;
c) Bearing capacity, FSbc: 2.5; and
d) Seismic stability, FSsei: 1.1.
Factors of safety with regard to sliding, overturning,
and eccentricity are not provided, as these failure
modes are not considered valid for SRS walls. The
overall external stability is governed by global and
compound stability analysis.
62.6 Internal Stability Design
Internal stability design of the RS component of an
SRS wall system should address the following
potential internal failure mechanisms for situation
when the available base width is more than
30 percent of the height. The design can also be
applied for other complex geometry situation, but
result shall be validated by finite element or
numerical modeling analysis. The design approach
for shored reinforced soil wall is based on LRFD
method and all resistance factors and factor of safety
are same as described in Chapter 4 except for
pull-out and bearing capacity checks.
a) Soil reinforcement rupture (elongation or
breakage of the reinforcements); and
b) Soil reinforcement pull-out.
The step-by-step process for internal design of
the RS component is summarized as follows:
a) Select the reinforcement type (inextensible
or extensible reinforcements) and trial
geometry for the RS wall;
b) Estimate the location of the critical failure
surface;
c) Calculate the maximum tensile force at
each reinforcement level for evaluation of
reinforcement rupture;
d) Calculate the required total tensile capacity
of reinforcements in the resistant zone; and
e) Calculate the pull-out capacity at each
reinforcement level within the resistant
zone with regard to pull-out.
Step 1: Select RS wall/slope type and wall geometry
The reinforced soil wall/slope system, including
type of reinforcement, facing and geometry, must be
selected to complete design. The calculations for
internal stability of the RS component differ
somewhat for extensible (geogrid or polymeric
straps) and inextensible (steel) reinforcements, as
discussed in Chapter 4.
Select vertical reinforcement spacing consistent
with the type of reinforced soil facing intended for
the application. The vertical reinforcement spacing
shall be as given in Chapter 4 and Chapter 5. For
ease of construction, consider constant vertical
reinforcement spacing except at top and bottom.
Step 2: Estimate the location of the critical failure
surface
The critical failure surface for wall can be using
Rankine’s active earth pressure theory within the
reinforced soil mass, considering the remaining
portion lies along the shoring and reinforced soil
fill interface. Use of the theoretical active failure
surface is consistent with current practice for design
of reinforced soil walls with extensible
reinforcements, and is considered sufficiently
conservative for design of such systems. Fig. 70 (A)
illustrates the conceptualized failure surface for
extensible reinforcements. Design for inextensible
reinforcements should be conducted using the
failure surface illustrated in Fig. 70 (B), which is
consistent with current design practice.
Step 3: Calculate the internal stability with respect
to rupture of the reinforcements
For shored reinforced soil walls, lateral pressures are
essentially the result of reaction of the reinforced
soil mass against the shoring wall, and are thus
internal to the reinforced soil mass. In consistent
with current design practice, internal design of the
reinforced soil wall component requires calculation
of lateral stresses, which are dependent on
reinforcement type (inextensible versus extensible).
For internal design of the RS component with
extensible reinforcements, active earth pressures are
conservatively apply and the maximum tensile
forces acting on each reinforcement layer are
calculated using the simplified method as described
in previous chapters.
At each reinforcement level, calculate the
horizontal stresses, σh, along the potential failure
line from the weight of the reinforced fill (γz), plus
uniform surcharge loads (q), and concentrated
surcharge loads (Δσv and Δσh):
σh = Kr σv + Δσh ...(7-1)
where the vertical stress, σv, is calculated as:
σv = γ⋅z + q + Δσv ...(7-2)
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and Kr is a function of depth (z) below the top of the
wall as shown in Chapter 4.
For wall face batters from vertical, the
equation 4-1 of Chapter 4 shall be referred.
The additional tensile forces due to seismic load for
the reinforced soil shored wall can be calculated as
per Section 4. The same load factor and resistance
factor shall be applied for the design as described in
Chapter 4.
Step 4: Calculate the required total tensile capacity
for pull-out check
The following procedure of pull-out calculation is
applicable when soil reinforcement is not
mechanically connected with shored wall. When soil
reinforcement is mechanically connected with soil
nails or anchor, the pull-out shall be checked only
for the nails or anchors. The bond strength
considered in design shall be validated by on site
pull-out test of soil nail/ground anchor as per
IS 11309. The internal design differs from design of
a conventional reinforced soil wall with regard to
pull-out of the reinforcements. The conventional
reinforced soil design requires that each layer of
reinforcement resist pull-out by extending beyond
the estimated failure surface. In the case of a shored
reinforced soil wall system, only the lower
reinforcement layers (that is, those that extend into
the resistant zone) are designed to resist pull-out for
the entire “active” reinforced mass.
FIG. 70 (A AND B) LOCATION OF POTENTIAL FAILURE SURFACE FOR INTERNAL STABILITY DESIGN OF
REINFORCED SOIL WALL COMPONENT WITH EXTENSIBLE AND INEXTENSIBLE REINFORCEMENTS RESPECTIVELY
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NOTES
1 For extensible reinforcements, ψ = 45 + φ/2; for inextensible reinforcements, ψ shall be as shown in Fig. 21 in Section 4.
2 Assume tension crack development and neglect forces N2 and S2.
3 Assume upper wedge (shown as gray) is in equilibrium.
FIG. 71 FREE-BODY DIAGRAM FOR CALCULATION OF REQUIRED TENSILE CAPACITY IN THE RESISTANT ZONE
The required total pull-out resistance (Tmax) of the
reinforcements within the resistant zone is
calculated as the pull-out force derived using the
simplified free-body diagram presented in Fig. 71
and the equation is as follows:
….(7-3)
where, H is the height of the reinforced soil wall,
γ is the unit weight of the reinforced fill, ψ and β is
the angle defined in Fig. 71, LW is the maximum
length of the truncated failure wedge, that is.,
reinforced length at the intersection of the shoring
wall and active wedge, φ’ is the friction angle for the
reinforced soil, q is the distributed surcharge load,
FV and FH is concentrated vertical and horizontal
loads respectively and H is the height of the
For the case where LW ≥ H tanβ, the full active
wedge would develop and the expression for Tmax is:
At each reinforcement layer within the resistant
zone, calculate the pull-out resistance following
standard design method, FPO.
…(7-4)
For the case where Lw = 0.3H, the expression for
Tmax is:
…. (7-5)
Step 5: Calculate the pull-out resistance of RS
reinforcements in the resistant zone.
The calculation of the pull-out resistance generally
follows traditional design methods. The primary
difference between calculation of pull-out resistance
for conventional reinforced soil walls and shored
reinforced soil walls is in the factor of safety. The
factor of safety against pull-out, FSp, should be
increased from 1.5 to 2.0 for aspect ratios of 0.4 or
less due to the potential for arching to develop.
Based on the reinforcement spacing(s) selected,
calculate the length of embedment (Lei) of each
reinforcement layer within the resistant zone:
IS 18591 : 2024
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Tmax =
( (𝐻−
𝐿𝑊
2 tan 𝛽
)+ 𝑞) + 𝐹𝑉
tan(ϕ҆ + β)
+ FH for LW ≤ H tan β
Tmax =
𝐻 tan β ( 𝐻+2𝑞)+2𝐹V
2 tan(ϕ҆+ β)
+ FH
Tmax =
3𝐻[ (𝐻−
3𝐻
20 tan β
)+𝑞]+𝐹V
10 tan(ϕ҆+ β)
+FH
γ
γ
γ
Lw
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The pull-out resistance of the reinforced soil wall
component of a shored wall system is considered
adequate if Tmax) calculated in previous section is
≤ the summation of pull-out resistance of all
reinforcement layers within the resistant zone
(Σ FPO).
However, the pull-out checks are not applicable
when all short length soil reinforcements are
mechanically connected with the nails or anchors.
Step 6: Calculate the connection between soil nail
and reinforcement
The connection strength between the soil nail and
soil reinforcement must be tested and the same shall
be adopted for design calculations.
The above simplified design approach is suitable for
shored wall having base width greater than or equal
to 0.3 H.
62.7 Internal Stability for Other Special Cases
of SRS Structure
For narrow or confined walls (base width 0.3 H),
the vertical overburden stress is likely less than the
unit weight of the overburden multiplied by the
wall height (σv γ H) due to arching effects, and
these effects require consideration for design of
stepped walls. For such special cases like narrow
width or stepped wall the structure can be designed
by same method and steep slope by allowable
stress design approach as described in Chapter 5
and also as indicated in Section 7, but the internal
stability checks for all special cases shall be
validated by finite element modeling or other
numerical methods.
62.8 External Stability Design
External stability design of the RS wall component
should address bearing capacity, settlement of the
foundation materials, compound and global stability
checks. Overturning and sliding are not applicable
as the stabilization against sliding and overturning is
provided by the shoring wall. Hydrostatic forces are
eliminated by incorporating effective internal
drainage into the design.
62.9 Bearing Capacity
The reinforced soil wall component should be
designed for stability against bearing capacity
failure. Unlike conventional wall, shored wall has
two possible modes of bearing capacity failure exist:
General shear and local shear failure.
62.9.1 General Shear
To prevent general shear bearing capacity failure,
the vertical stress (σv) at the base of the wall should
not exceed the allowable bearing capacity (qa) of
the foundation soils:
….(7-6)
The vertical stress, σv, acting at the base of the RS
wall component for the case presented in Fig. 72
with horizontal backfill and traffic surcharge is
given by:
….(7-7)
FIG. 72 CALCULATION OF VERTICAL STRESS AT FOUNDATION LEVEL
124
IS 18591 : 2024
qult
F Sbc
σv ≤ qa =
W1 + (q . LB)
LB
σv =
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Calculate the ultimate bearing capacity (qult) using
classical soil mechanics methods:
….(7-8)
where cf is the cohesion of the foundation soils, γf
is the unit weight of the foundation soils, and Ncq
and Nγq are dimensionless bearing capacity
coefficients. No check for eccentricity is
recommended, as eccentricity effects are minimal
due to the presence of the shoring wall.
62.9.2 Local Shear
Local shear is characterized by local “squeezing” of
the foundation soils when retaining walls are
constructed on soft or loose soils (that is,
development of the classic bearing capacity failure
surface does not occur). This is applicable for shored
type of retaining wall due to shorter base width of
the structure. Ground improvement of the
foundation soils should be incorporated if adequate
support conditions are not available.
62.9.3 Settlement
62.9.3.1 The shored reinforced soil structure is little
more sensitive to settlement that conventional
reinforced soil wall/slope. Settlement within the RS
mass itself must be considered. Significant
settlement of the reinforced soil mass is not likely to
occur where compacted select granular fill is used
for the reinforced fill zone. However, a tension crack
behind the reinforced soil mass at the top of the wall
may result if the reinforced fill zone is constructed
of material that does not meet recommended
specifications for reinforced fill, as discussed in
Section 7.
62.9.3.2 Settlements external to the reinforced soil
mass should be considered. The RS wall base width,
L, may be considerably shorter for the reinforced
soil component of a shored wall system than for a
conventional reinforced soil wall. The narrow RS
wall component may be more vulnerable to
differential settlement if the foundation is
compressible, thus producing an exaggerated
outward rotation of the RS mass and development of
a tension crack above the interface. Extended upper
reinforcement layers are recommended to mitigate
this effect.
62.9.3.3 Providing nominal facing batters for both
the shoring wall interface and reinforced soil face
are expected to help mitigate differential settlement
to certain extend. However, the total settlement
shall be limited to within 150 mm for discrete panel
and other flexible type facing system. Use of rigid
facing system (non-compressible) like full height
panel shall not be permitted for such structures.
62.9.3.4 As discussed in previous sections, one or
more of the following are recommended for shored
wall/slope design:
a) Overlap at least two upper reinforcement
layers over the shoring wall section to a
minimum length of 0.6 H or 1.5 m beyond
the shoring, whichever is greater. This is
when the available based width is
minimum 30 percent of the height of the
wall/slope;
b) Employ mechanical connection between
the wall reinforcing layers and shoring wall
components;
c) Use partial shoring construction when the
lower portion of the reinforced wall is
retained by shoring with longer
reinforcements at the upper extent of the
wall; and
d) The following additional details shall be
considered to reduce effects from
differential wall settlement behaviour:
1) Construction of a stepped shoring wall
or interface; and
2) Foundation improvement (if required)
prior to construction of the RS
component.
62.10 Design of Shoring Wall Component of a
Shored Wall System
The shoring component of the shored wall system
must be compatible with the reinforced wall
component. This is primarily a geometric concern,
but global stability considerations may also govern
the design, and may even require adjustment of
either the shoring component or the reinforced soil
component to provide for an effective wall/slope
system design.
Soil nailing is a common shoring method for sites
where SRS wall systems are applicable. Soil nail
walls also have an advantage with respect to global
stability in that they reinforce the soil behind the
shoring wall in much the same way that RS wall
reinforcements do for the RS mass. As a result, soil
nail walls are advantageous as the shoring method
for use with SRS wall/slope systems is given in the
Table 37.
IS 18591 : 2024
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qult = cf Ncq + 0.5 LB γf Nγq
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Table 37 Recommended Shored Wall Construction Tolerances (Hard Facing System)
(Clause 62.10)
Sl No. Description Requirement
(1) (2) (3)
i) Wall batter ± 50 mm per 3.0 m of wall height and
1 percent for the overall wall height.
ii) Wall height ± 25 mm per 3.0 m of wall height and a
maximum of 100 mm.
iii) Horizontal and vertical
alignment
± 50 mm at any point in the wall when
measured with a 3.0 m straightedge.
iv) Separation of facing mat Outside of facing mat shall be within 40 mm
from MSE facing fill at all locations.
v) Reinforcement elevation Within 50 mm above the design elevation and
within 50 mm above the corresponding
connection elevation at the wall face.
Reinforcement shall not be placed below
corresponding connection elevation.
vi) Reinforcement inclination Within 2 percent from horizontal.
vii) MSE reinforcement to
shoring wall face
± 50 mm
SECTION 8
DESIGN OF BASAL REINFORCEMENT
63 INTRODUCTION
63.1 The design and construction of embankments
on good bearing stratum do not pose any problems.
However, soft soil conditions in the foundation
layers, create several complexities for the designer
and field engineer. Construction of embankments on
soft clay or organic peat can be critical because these
soils have very low strength and high
compressibility. When faced with the situation of
constructing an embankment on a soft subsoil, the
following problems may be encountered:
a) Failure of soft subsoil in shear (failure in
bearing capacity);
b) Stability of embankment (lateral sliding
and rotational stability); and
c) High compressibility and settlement of
embankment (settlement).
63.2 Embankments constructed on soft foundation
soils tend to spread laterally because of lateral earth
pressures acting within the embankment. These
earth pressures cause horizontal stresses at the base
of embankment that must be resisted by the
foundation soil. If the foundation soil does not have
adequate shear resistance, failure can happen.
Properly designed horizontal layers of high strength
geosynthetic reinforcement layers increase the
stability and prevent such failures. If a geogrid
(see IS 17373) or geocell [see IS 17483 (Part 1)]
layer is used as a basal reinforcement a nonwoven
geotextile separator needs to be provided for
filtration and prevent contamination of the first lift if
it is an open-graded or similar type soil. Separator
layer is not required beneath the first lift if it is sand,
which meets soil filtration criteria.
63.3 Fine grained soils are classified based on
undrained shear strength as ranging from very soft
to hard:
Sl No. Consistency Undrained Shear
Strength (kPa)
(1) (2) (3)
i) Very stiff or hard 400
ii) Stiff to very stiff Above 200 to 400
iii) Stiff Above 100 to 200
iv) Medium Above 50 to 100
v) Soft 25 to 50
vi) Very soft 25
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63.4 Reinforcement Using Geosynthetics
63.4.1 To reduce the subsoil stresses and
improvement in drainage, replacement of poor
subsoil with good quality granular soil as per
Section 3 (except pond ash) for shallow depths, use
of geosynthetic reinforcement at the base of the
embankment are often carried out. Construction of a
basal platform/basal mattress to spread the loading
on the ground prevents base failure and may reduce
settlements.
63.4.2 The geosynthetic, used for basal
reinforcement has the main function of reinforcing
the soil and is placed in between two layers of gravel
or sand which serves as the drainage layer as well as
the frictional layer that enables mobilization of
tensile force in the reinforcement. The geosynthetic
reinforcement along with the granular fill acts as a
stiff working platform for ease of moving the
construction equipment at the site.
63.4.3 A layer of gravel/granular fill shall be placed
on top and bottom of reinforcement for proper
interaction and it shall be minimum 200 mm. It is
also necessary to provide a nonwoven geotextile as
a separation layer at the interface of soft subsoil and
the gravel/granular base layer.
63.4.4 The use of reinforcing layer serves the
following functions:
a) Construction is facilitated as machinery
can move easily above the reinforcement
for placing the fill;
b) The tensile reinforcement provides
improvement in the rotational stability of
the embankment;
c) Improvement in lateral sliding;
d) Provide good drainage layer;
e) Minimize the differential settlements; and
f) An improvement in embankment
performance due to increased uniformity of
post construction settlement.
63.4.5 Geocells are three-dimensional, permeable,
polymeric (synthetic or natural) honeycomb, or
similar cellular structure, made of linked strips of
geosynthetics. The strips are ultrasonically joined
together to form interconnected cells that are infilled
with soil. In some cases, 0.5 m to 1 m wide strips of
polyolefin geogrids have been linked together with
vertical polymeric rods used to form deep 3-D
mattress called as geo-mattresses.
63.4.6 For basal reinforcement, a product with high
tensile strength, low elongation and low creep is
required. Geo-composite, in which the reinforcing as
well as separating and draining materials are bonded
together, can be used for basal reinforcement where
drainage function is required. A nonwoven
geotextile bonded to a geogrid provides in-plane
drainage while the geogrid provides tensile
reinforcement. Such geotextile-geogrid composites
are used for better drainage of low-permeable soils.
63.5 Areas of Application
For the construction of reinforced embankments
over soft and very soft foundation soils the
techniques in use may be divided into one of the
following two categories:
a) Category 1: The techniques where the
reinforcement is used to control stability of
the embankment, without reducing
settlement:
1) Basal reinforcement beneath
embankment;
2) Basal mattress reinforcement; and
3) Basal reinforcement with vertical
drains.
The standard covers the design aspects for basal
reinforcement over soft embankment, embankments
over voids and basal mattress reinforced
embankments.
b) Category 2: Pile or stone column or sand
column below embankment can be
combined with basal reinforcement as part
of a foundation stabilization system to
control stability and prevent or limit
settlement of the embankment:
1) Stone columns or compacted granular
columns with basal reinforcement.
Category 2 application is not covered in this
standard and BS 8006-1 or EBGEO can be referred
for this application.
64 DESIGN OF BASAL REINFORCED
EMBANKMENTS OVER SOFT SUBSOIL
64.1 The design of embankment on soft ground
depends upon the shear resistance of the foundation
soil in which bearing capacity of the foundation soil
may govern the design. The inclusion of
geosynthetic reinforcement at the base of the
embankment will help to reduce the shear failure in
embankment as well as in the foundation soil.
64.2 Basal reinforcement stabilizes an embankment
over soft soil by:
a) Prevention against lateral sliding;
b) Extrusion of foundation;
c) Rotational failure; and
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d) Reduction in differential settlement.
64.3 The basal reinforcement may be placed at
foundation level to prevent shear failure both in the
embankment fill and in the foundation soil. It is
important to consider that the stability of an
embankment on soft soil is most critical during
construction, because the relatively low
permeability of the soft foundation soil does not
permit adequate degree of consolidation during the
construction period.
64.4 At the end of construction, the embankment
loading has been applied, but the gain in shearing
resistance of the foundation due to consolidation
might be insufficient for stability. Basal
reinforcement stabilizes an embankment over soft
ground by preventing lateral spreading of the fill and
overall rotational failure. Basal reinforcement also
stabilises the foundation soil against lateral
extrusion. This stabilizing force is generated in the
reinforcement by shear stresses transmitted from the
foundation soil and fill, which place the
reinforcement in tension. It has also been
experienced that the reinforcement can also partially
reduce the differential settlement due to better
distribution of stress over the soft soil.
64.5 The duration of the tensile strength requirement
from the basal reinforcement depends upon the rate
of gain in shear strength due to consolidation. The
design life of the reinforcement may be considered
in general as equal to the time required to achieve
90 percent consolidation. Generally, the maximum
design working load is experienced at the end of
construction of the embankment.
64.6 Basal reinforcement shall be designed for
various modes of failure as follows:
a) Bearing capacity;
b) Rotational stability of the embankment;
c) Lateral sliding stability of the embankment
fill;
d) Foundation extrusion; and
e) Overall stability.
FIG. 73 EMBANKMENT REINFORCED WITH GEOSYNTHETICS
FIG. 74 USE OF GEOSYNTHETIC AS A BASAL REINFORCEMENT
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a) Bearing capacity
FIG. 75 VARIOUS MODES OF FAILURE
IS 18591 : 2024
129
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64.7 Bearing Capacity Failure
The basal reinforcement is assumed to act as a stiff
layer which helps in distributing the embankment
load onto the sub soil evenly. Soft soils gain strength
due to consolidation which is a time dependent
mechanism.
Following formula is used to calculate the ultimate
bearing capacity of the foundation.
Qult = Cu.Nc ….(8.1)
where
Cu = undrained cohesive strength of the soil in
kN/m2
; and
Nc = bearing capacity factor.
For embankment over soft subsoil, Nc can be
calculated as:
Nc = 5.14 for B/D ≤ 2 ….(8.2)
Nc = 4.14 + 0.5 B/D for B/D ≥2 ….(8.3)
where
B = the bottom width of embankment in meter;
and
D = the depth of soft soil in meter.
A factor of safety of 1.5 for bearing capacity at the
end of construction shall be achieved where no
ground improvement implemented. If the factor of
safety of soft soil is not sufficient then ground
improvement techniques like preconsolidation,
stone columns, stage construction can be used along
with the basal reinforcement. Factor of safety of 1.3
can be considered satisfactory at the end of
construction for basal reinforcement combined with
other ground improvement techniques. Factor of
safety of 1.5 at the end of consolidation period shall
be achieved.
64.8 Rotational Stability
64.8.1 Rotational stability of the embankment shall
be carried out using method of slices. The tensile
force required (Tg) for rotational stability of
embankment determined from method of slices and
this shall be long term design tensile strength of
reinforcement as per 64.13.
The maximum tensile force Tg to be resisted by the
basal reinforcement should be the greater of:
a) the maximum tensile force needed to resist
the rotational limit state per metre run; and
b) the sum of the maximum tensile force
needed to resist lateral sliding per metre run
and the maximum tensile force needed to
resist foundation extrusion per metre run.
64.8.2 Tensile strength of reinforcement calculated
considering various reduction factors for
reinforcement as per IS 17365. Factor of safety for
the various failure surfaces must be analysed. A
computer program or software is preferable for the
analysis of critical failure surfaces as manual
calculations are time consuming.
64.8.3 A minimum factor of safety of 1.4 shall be
adopted for rotational stability analysis. The factor
of safety of the reinforced embankment can be
calculated using following formula:
ΣMr + Tg d
...(8.4)
where
Mr = summation of resisting moment of all
slices in kN-m/m;
Md = summation of driving moment of all
slices in kN-m/m;
Tg = required tensile force kN/m; and
d = vertical distance between the centre of
slip circle and horizontal reinforcement
layer in meter.
64.8.4 It is recommended to do global stability check
using noncircular slip surface as well, in case of thin,
embankments founded on deposits of very soft soil.
When thin, soft clays are present below embankment
failure mechanism will be due to extrusion than
overall stability.
64.9 Lateral Sliding
This check shall be performed considering the
embankment fill should not slide over the
reinforcement. The basal reinforcement must resist
the outward horizontal thrust of the embankment fill.
The minimum tensile strength required to resist
lateral sliding shall be worked out as below:
--(8.5)
---(8.6)
IS 18591 : 2024
130
FSR =
ΣMd
Tls = 0.5 Kaq H2 + Kaq H
𝐾a = [
sin (β − ϕ)
(sinβ)2+ sinϕ.√sinβ
]
2
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FIG. 76 ROTATIONAL STABILITY
FIG. 77 LATERAL SLIDING OF EMBANKMENT OVER BASAL REINFORCEMENT
A minimum value of factor of safety as 1.5 for lateral
sliding shall be achieved:
---(8.7)
where
W = 0.5 × de × H × Le;
de = the density of embankment fill in kN/m3
;
Le = the reinforcement bond length in meter
(refer Fig. 8);
α = the interaction coefficient relating the
embankment fill and reinforcement
material bond angle, which should be
specified in the certification document
[for example, BBA, NTPEP (AASTHO)].
In case of absence of certification, it
should be limited to 0.5;
Sometimes the length of reinforcement Le required
for lateral sliding is more than right of way available
and embankment width at bottom. In such case
anchorage blocks shall be provided made of
concrete, sandbag, gabion or wrap around ,etc
(refer Fig. 78).
ϕ = the angle of internal friction for
embankment fill;
Ka = the active earth pressure coefficient
for embankment fill;
H = the height of embankment in meter;
and
q = the surcharge intensity over the
embankment in kPa.
IS 18591 : 2024
131
β = slope angle (tanβ = 1: n);
𝐹𝑆s =
𝑊α tanϕ
𝑇ls
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FIG. 78 ANCHORAGE ARRANGEMENT FOR BASAL REINFORCEMENT
These sections must also be investigated for sliding
of the embankment above the wrap-around and for
sliding of the embankment above the reinforcement
layer:
---(8.8)
---(8.9)
where
FS = the factor of safety (minimum 1.35);
FIG. 79 EMBANKMENT SLIDING ABOVE THE REINFORCEMENT LAYER
Pah or Tls = the lateral thrust relative to
embankment height H;
Pah3 = the lateral thrust relative to
embankment height h3;
RO = the resistance between the
embankment fill material and
the top of the geosynthetics;
R3 = the resistance between the
embankment fill material and
the top of the geosynthetics
(relative to the length h3/tanβ);
and
RB = the long-term design strength
(LTDS) of the reinforcement
layer as per 64.13.
.
IS 18591 : 2024
132
FS =
RO + Minimum of (R3, RB)
Tls or Pah
FS =
R3
Pah3
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FIG. 80 EMBANKMENT SLIDING ABOVE THE WRAP-AROUND/ANCHOR BLOCK
The lateral earth pressures from soil dead weight and
live loads on the embankment crest are adopted as
actions:
…(8.10)
where
Ka = the active earth pressure coefficient for
embankment fill (Eq 8.6), which depends
on slope angle () and friction angle of the
soil (); and h3 is the height of the
embankment above wrap around.
Friction resistance on top of the geosynthetic R3
The friction resistance between the embankment fill
material and the geosynthetic is:
where, f1g friction coefficient between the
embankment fill material and the geosynthetics.
This shall be determined by direct shear test or
pullout tests. In absence of test results maximum
value of 0.5 tan ϕ shall be considered.
Friction resistance on top of the geosynthetics RO
The friction resistance between the embankment fill
material and the geosynthetics is:
64.10 Foundation Extrusion
64.10.1 It should be noted that the geometry of the
embankment induces outward shear stresses within
the soft foundation soil, and where the foundation
soil is soft and of limited depth the outward shear
stresses can induce extrusion of the foundation.
64.10.2 High lateral stresses in a confined soft
stratum beneath an embankment could lead to a
lateral extrusion. The failure of the foundation
should be anticipated if γ fill x Hfill 3 x C, and a
weak soil layer exists beneath the embankment to a
depth that is less that the width of the embankment.
When the depth of the soft layer is greater than the
base width of the embankment, general bearing
capacity and overall stability may govern the design.
64.10.3 Further, to prevent this extrusion the side
slope length of the embankment Ls should be great
enough to prevent mobilization of these outward
shear stresses.
64.10.4 The failure mechanism assumes the lateral
extrusion of foundation soil from beneath the
embankment. To prevent this failure mechanism
from occurring, the outward foundation movement
should be limited by developing adequate lateral
confinement over a sufficient surface area at the
underside of the basal reinforcement (refer Fig. 81).
To achieve these following conditions should be
satisfied:
a) the overall shearing resistance on the
underside of the reinforcement should be
sufficient to resist the lateral loads
developed in the foundation soil; and
b) the basal reinforcement should have
sufficient tensile strength to withstand the
tensile loads induced by the shear stress
transmitted from the foundation soil.
64.10.5 To prevent foundation extrusion, the
following relationship should apply:
Rha ≤ Rhp + Rs + RR
Rha = horizontal force causing foundation extrusion;
Rhp = horizontal force due to passive resistance of
the foundation;
RS = horizontal force due to the shear resistance of
the foundation soil at depth zC; and
RR = horizontal force due to the shear resistance of
the foundation soil at the underside of the
reinforcement.
IS 18591 : 2024
133
Pah3 = γ 0.5 h3 h3 Ka + q h3 Ka
𝑅3 =
1
2
γ (
ℎ3
𝑡𝑎𝑛β
) ℎ3 𝑓1g
𝑅𝑂 =
1
2
𝐻
𝑡𝑎𝑛β
) 𝐻 𝑓1g
...(8.11)
...(8.12)
γ (
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FIG. 81 FOUNDATION EXTRUSION STABILITY ANALYSIS
64.10.6 A sensitivity analysis using different values
of zc should be performed to determine the
minimum side slope length Ls needed to prevent
foundation extrusion. The depth of zC should be
limited to a maximum of twice the height of the
embankment.
Minimum necessary side slope length Ls to be
determined as follows:
…(8.13)
where
Cu = undrained shear strength of the soft
foundation layer;
zc = depth of the soft foundation layer when
the foundation is of limited depth with
constant undrained shear strength with
depth; and
a’bc = interaction coefficient relating the
soil/reinforcement adherence to Cu.
64.10.7 Similarly, an expression exists for the case
of a foundation soil, with shear strength linearly
increasing with depth, where the minimum factor
of safety is given at a critical depth zc below the
ground surface, which may be determined by:
---(8.14)
where
n = side slope of the embankment; and
 = increase in shear strength per unit depth.
64.10.8 The minimum required side slope length Ls
may be determined as follows:
…(8.15)
64.10.9 The tensile load generated in the basal
reinforcement Trf per metre run due to outward
foundation shear stress may be taken from:
…(8.16)
where
Le = length of the reinforcement required;
cuo = undrained shear strength of the foundation
soil at the underside of the reinforcement;
and
FS = minimum factor of safety of 1.3.
64.10.10 Care should be taken in the choice of the
value of a′
𝑏𝑐 the adherence coefficient at the
reinforcement/soft foundation soil interface; the
magnitude of a′
𝑏𝑐 is related not only to the surface
characteristics of the reinforcement but also to the
strain in the reinforcement compared to the strain in
the soft foundation.
134
IS 18591 : 2024
𝐹𝑆 =
𝐿𝑠 ≥
(γ H + 𝑞 − 4𝐶u) 𝑧c
(1 + 𝑎′
bc) 𝐶u
cuo 𝐿e
𝑇rf
𝐿𝑠 =
[γH + w − (2cu + zc) 2] zc
(1 + abc) cu+ zc
Z c = √
(1+ 𝑎
҆
bc) 𝐶u𝑛 𝐻
2𝜌
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64.11 Seismic Loading
For analysing the full height embankment,
pseudo-static limit equilibrium analysis can be
performed using either a total or an effective stress
analysis. Problems of estimating pore water
pressures induced by cyclic shearing are avoided by
using a total stress analysis. In the pseudo-static
limit equilibrium analysis, a seismic coefficient is
used to represent the effect of the inertia forces
imposed by the earthquake upon the potential failure
mass. Simplifications made in using the
pseudo-static approach to evaluate seismic slope
stability include replacing the cyclic earthquake
motion with a constant horizontal acceleration equal
to KH x g, where KH is the seismic coefficient which
shall be considered 0.5 Z (zone factor Z as per
Table 2 of IS 1893-1), and g is acceleration of
gravity:
---(8.17)
where
FS = factor of safety (minimum 1.1);
Mr = summation of resisting moment of
all slices in kN-m/m;
Md = summation of driving moment of all
slices in kN-m/m;
Tgs = tensile force of reinforcement
needed in the reinforcement for
seismic case kN/m (ignoring
reduction factor for creep as seismic
loading is applied for short
duration); and
d = vertical distance between centre
of rotation and horizontal
reinforcement layer in m.
64.12 Overall Stability
For embankments founded on deep deposits of very
soft soil overall stability should be checked to
ensure deep-seated rotational failures (refer
Fig. 75). Conventional slip surface analyses may be
used to examine this mode of failure.
64.13 Design Tensile Strength of Reinforcement
64.13.1 The long-term tensile strength of the
reinforcement can be calculated by considering the
short-term strength of the reinforcement and the
reduction factors, is given below:
Tal = Tult/ (RFCR × RFID × RFW × RFCH × fs) …(8.18)
where
Tal = long-term tensile strength of the
reinforcement in kN/m;
Tult = ultimate tensile strength (short
term strength/characteristic
strength) from a standard in
isolation wide width tensile test in
kN/m;
RFID = reduction factor for installation
damage;
RFCR = reduction factor for creep;
RFCH = reduction factor against
chemical/environmental effects;
RFW = reduction factor to allow for
weathering during exposure prior
to installation or of permanently
exposed material;
fs = factor for extrapolation of data;
and
RFD = cumulative reduction factor
(RFCH × RFW) is referred
for reduction for durability.
64.13.2 All the above reduction factors shall be
determined as per IS 17365. However ambient
temperature in India is high, creep factor at 30 °C
and 40 °C shall also be provided besides the
reduction factors at 20 °C.
64.13.3 Long term design strength of reinforcement
shall be meet the rotational stability, overall
stability, lateral sliding, and foundation extrusion.
The ultimate tensile strength of the reinforcement
shall be decided as per procedure presented below.
64.13.4 Force in the reinforcement (Tf) shall be
maximum of Tg, Tgs and Tls + Trf. and Tf shall be
greater than or equal to Tal. Strain in reinforcement
for short term as per 64.13 shall be determined for
stress strain curve at Tal force. Long term strain as
per 64.13 shall be determined from isochronous
curves and shall be within acceptable limits.
65 EMBANKMENTS OVER VOIDS
65.1 Areas of Application
The following should be considered in dealing with
areas prone to subsidence.
a) Subsidence normally results from the
collapse of a void below the ground
surface. Subterranean voids can arise from
natural processes (for example, soil erosion
in karstic areas) or from man-made
processes (for example, ground water
pumping or underground mining);
IS 18591 : 2024
135
FS =
 Mr + Tgs d
 Md
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b) The consequences of subsidence occurring
beneath structures can range from a loss of
serviceability to total collapse; and
c) Embankments, fills and pavements are
essentially flexible structures. Thus, the
techniques used to minimize damage
resulting from subsidence normally involve
confining the vertical differential
displacement of the structure to within
predetermined tolerances. From this point
of view either rigid foundation rafts, or
reinforced soil techniques have proved
effective.
65.2 Design
65.2.1 Reinforcement may be used to limit the
amount of surface deformation caused by
subsidence (see Fig. 82). A void developing
beneath a reinforced embankment sometime after
construction may be repaired by filling the void with
grout in which case the reinforcement should act
temporarily. If the void is left open the
reinforcement should be specified to act for the
remaining design life of the structure. Voids under
high-cost structures (for example, motorway
embankments) should be filled, while for lower cost
structures (For example, low trafficked pavements)
the cost of filling the voids may not normally be
justified. Reinforcement may be utilized in two
different ways: Internal reinforcement within the
embankment structure and reinforcement at the base
of the embankment. For internal reinforcement,
several layers of reinforcement may normally be
included within the height of the embankment; the
analysis of this technique is complex.
65.2.2 The formulation contained are based on two
principal assumptions:
a) Constant volume of soil in “zone of
depression”; and
b) No arching within the embankment fill.
65.2.3 Both assumptions can lead to conservatism in
design. The assumption of no arching in the
embankment fill may be taken as valid for low
embankment height to void size ratios (H/D 1)
and hence the “zone of deformation” depicted in
Fig. 82 of an inverted, truncated wedge or cone
influencing the reinforcement is valid. Strain limits
in the reinforcement should be controlled, at the
base of the zone of deformation, to limit depression
at the embankment surface. By considering the
geometry of the zone of influence, ignoring arching
and assuming a constant volume and equating the
volumetric movement of the reinforcement and the
volumetric movement of the soil, a relationship may
be presented for the maximum allowable
reinforcement strain.
FIG. 82 REINFORCEMENT IN LIMITING SURFACE DEFORMATIONS DUE TO SUBSIDENCE
IS 18591 : 2024
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65.2.4 Void Diameter
The determination of a suitable design value for the void diameter should normally be based on experience of
similar conditions, a subterranean survey, and/or a probabilistic approach. A conservative value should be
assumed because of the uncertainties of future subsidence, and the consequent risks involved.
FIG. 83 PARAMETERS USED TO DETERMINE REINFORCEMENT
where
ds/Ds = maximum allowable differential
deformation occurring at the surface
of the embankment or pavement;
ds = depression at surface;
d = depression at reinforcement;
D = design diameter of the void;
H = height of embankment; and
θd = angle of draw of the embankment fill
(which is approximately equal to its
peak friction angle).
In order to optimize the bond length and slippage, an
anchored system may be employed. The anchors at
the end of both the ends of reinforcement would
mobilize the required force in the relatively short
length of reinforcement. The design of anchored
system is not covered by this document.
65.2.5 Allowable Surface Deformation
The degree of acceptable surface deformation may
be estimated dependent on the design philosophy for
the supporting reinforcement. The reinforcement
may be designed to support the overlying
embankment for the design life of the infrastructure
and the surface settlement to remain within
acceptable serviceability limits. Similarly, the
reinforcement may be designed to support the
embankment for a shorter period of time allowing
for some form of remedial measures to infill/reduce
the void; the latter approach is likely to require some
form of detection and remediation protocol to be
established by the infrastructure owner/operator.
For principal roads, the maximum differential
surface deformation (ds/Ds) should be limited to
1 percent. For non-principal roads, differential
settlement should be limited to 2 percent. For
consideration beneath railway lines, more stringent
allowable deflections should be considered; these
may be derived from the maximum allowable cross-
rail differential movements to prevent a twist fault
or derailment. The allowable limit may be decided
based on agreement between designer and owner of
the project.
65.2.6 Tensile Strength, Strain and Bond Length
Tensile strength: For extensible reinforcements
(for example, polymeric) the tensile load Trs in the
deflected reinforcement should be taken to be:
where
Trs = tensile load in the reinforcement per metre
“run” which shall be greater than or equal
to long term design strength as per 64.13;
IS 18591 : 2024
137
𝑇rs = 0.5 𝜆 (𝛾 𝐻 + 𝑞)𝐷√1 +
1
6
…(8.19)
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 = a coefficient dependent on whether the
reinforcement support is to function as a
one-way ( = 1) or two-way load
shedding system ( = 0.67);
= unit weight of the embankment fill;
H = height of the embankment; and
 = strain in the reinforcement which is less
than or equal to max.
Strain: The deflected shape of the reinforcement
spanning the void may be approximated to a
parabola, where the maximum allowable strain in
the reinforcement is:
For plane strain conditions (that is, long voids);
For axisymmetric conditions (that is, circular voids);
Bond length: To generate the tensile load Trs in the
reinforcement adequate bond should exist between
the reinforcement and the adjacent soil. The
minimum reinforcement bond length Lb needed to
carry Trs should be
…(8.22)
where
h = average height of fill over the bond
length of the reinforcement;
= unit weight of the embankment fill;
a’1 = interaction coefficient relating the
soil/reinforcement bond angle to tan ɸ1
on one side of the reinforcement; and
a’2 = interaction coefficient relating the
soil/reinforcement bond angle to tan ɸ2
on the opposite side of the
reinforcement.
66 BASAL MATTRESS REINFORCED
EMBANKMENTS
66.1 Basal mattress, which is a three-dimensional
structure formed from a series of interlocking cells,
may be used as reinforcement below embankments.
The use of a mattress at the base of an embankment
is shown schematically in Fig. 84.
FIG. 84 REINFORCEMENT USED TO CONTROL ONLY STABILITY OF EMBANKMENT
IS 18591 : 2024
138
…(8.20)
...(8.21)
Lb ≥
Trs
γh (a'1 tanϕ1 + a'2 tanϕ2)
γ
γ
Ɛmax =
8(
𝑑𝑠
𝐷𝑠
) (𝐷+
2𝐻
𝑡𝑎𝑛Ɵ𝑑
)
3 𝐷4
Ɛmax =
8(
𝑑𝑠
𝐷𝑠
) (𝐷+
2𝐻
𝑡𝑎𝑛Ɵ𝑑
)
3 𝐷6
4
6
2
2
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66.2 A basal mattress reinforcement may be
incorporated to interact with the embankment and
produce:
a) A good adhesive interface between the soft
foundation and the contained granular fill
of the mattress; and
b) A relatively stiff platform to ensure both an
even distribution of load onto the
foundation and a more uniform stress field
within the soft foundation soil.
66.3 These properties enable the basal mattress to
influence the deformation of the soft foundation and
hence may be used to mobilize its maximum shear
strength and bearing capacity. While the basal
mattress may be analysed using the procedure
detailed in 64.7 to 64.12, a method based on slip
line fields for the analysis of foundation stability
should generally be used (see Fig. 85, Bush et al,
1989). The plastic deformation of the soft
foundation soil should be examined using the slip
line fields and the ultimate bearing capacity
calculated. The overburden stresses and the
available bearing capacity should then be compared
to ensure that equilibrium conditions are satisfied.
The basal mattress may be checked to ensure it can
support the tension generated by the outward thrust
of the embankment fill.
66.4 The basic assumption may be made that normal
slip failure mechanism cannot form due to the
strength and stiffness of the cellular mattress; when
the thickness of the subsoil is relatively thin
compared with the embankment base width. The
prandtl type punching failure cannot take place and
plastic flow in the soft foundation layers becomes
the critical mechanism.
NOTE — The soft underlying soil is essentially sandwiched
between two, rigid surfaces giving a situation like that of the
compression of a block between, rough, rigid parallel
platens.
66.5 It should be noted that the basal mattress
technique can be particularly effective with
relatively thin, soft foundation layers where the ratio
of embankment width to depth of soft soil is greater
than four.
66.6 Once the bearing capacity conditions have been
satisfied, the tensile loads in the reinforcement
forming the basal mattress may be determined by
using a method described in Jenner et al. (1988),
which examines the stress condition at the underside
of the mattress to calculate the lateral loads that need
to be resisted by the reinforcement allowing for the
resistance provided by the foundation soil.
NOTE — The correct installation and construction
sequence of the cellular mattress is paramount to its
performance. The installation procedure for cellular
mattresses is described in cow land and Wong (1993).
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Key
1 Embankment
2 Basal mattress
3 Soft foundation
4 Slip line field
5 From geometry of slip line field
6 Value at edge of rigid head from slip line field
7 Average stress across rigid head
8 From geometry of slip line field
FIG. 85 STABILITY ANALYSIS FOR BASAL MATTRESS REINFORCEMENT
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67 STABILITY ANALYSIS OF
EMBANKMENTS WITH HDPE GEOCELLS
AS BASAL REINFORCEMENTS
67.1 When a soil structure is constructed on weak
soil with geocells along the subgrade level as basal
reinforcement, the slip surface will have to pass
through the geocell reinforced section. The
mechanism for resisting shear failure when geocells
are used as basal reinforcement is different from
geogrids. The polymeric geogrids are two
dimensional and are relatively flexible. The geocells
are on the contrary, stiffer three-dimensional panels
with the straps placed orthogonal to the plane of the
panel. The stiffness furthermore increases with
infilling of non-plastic soil. Hence the geocell layers
below the soil structure behaves as a stratum with
higher shear strength. Fig. 85 illustrates the slip
circle failure surface through the geocell layer.
Stability analysis of embankment with geocell as
basal reinforcement shall be carried out as per
procedure 64.7 to 64.12 and geocell properties shall
be considered as explained below.
67.2 For geocells, the philosophy of considering the
tensile force of reinforcement .
will be governed by
the orientation of the geocells with respect to the
embankment cross section:
a) When the straps of the geocell are oriented
along the cross section of the embankment
— Fig. 86 (A), lateral forces from the
embankment are transferred to the infill
through friction, and the infill transfers
these forces to the geocell expanded
profile. Hence the design tensile strength
of the straps is to be considered. It is to be
All the cells of the geocells are infilled. The infill,
being totally confined, will transfer the forces to the
geocell straps. With the transfer of forces, the weld
seam also is stressed. Hence the weld seam strength
is also significant.
b) When the straps of the geocell are oriented
along the embankment longitudinal axis —
Fig. 86 (C), as in the previous case, lateral
forces from the embankment are
transferred to the infill through friction and
the infill transfers these forces to the
geocell profile. However, in this case,
tensile resistance from the straps will not
be significant and the lateral forces
(other than the component resisted by
friction between infill and underlying soil)
will be resisted essentially by the geocell
weld seams. In this case, weld seam peel
strength should be determined by
“Method B” as per IS 17369 (Part 1) shown
schematically in Fig. 86 (D).
FIG. 86 (A) GEOCELL STRAPS ALONG EMBANKMENT LATERAL
DIRECTION
FIG. 86 (B) WELD SEAM PEEL STRENGTH -
METHOD A
T needs to be checked not only with respect to the
design tensile strength of the perforated strap, but
also the weld seam peel strength of the geocell. In
this case, weld seam peel strength should be
determined by “Method A” as per IS 17369
(Part 1). The “Method A” style of testing is shown
in Fig. 86 (B).
noted that the strap is parallel to the lateral
force exerted by the embankment over
some length and roughly at about 45° over
some other length. Hence the average
resistance offered by the straps alone could
be taken as 0.85 ;
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FIG. 86 (C) GEOCELL STRAPS ALONG EMBANKMENT
LONGITUDINAL DIRECTION
FIG. 86 (D) WELD SEAM PEEL STRENGTH -
METHOD B
67.3 It may be noted that the stresses on the welded
seams will be reduced owing to the confined
infilling in the cells. The reduction can be significant
but difficult to determine at this juncture. Not much
work has been performed regarding geocells
stressed along the plane of the panel in either
direction.
67.4 The geocell is a three-dimensional
geosynthetic material with interconnected
curvilinear rhomboidal cells. The interconnected
cells form a cellular confinement system when
expanded and infilled with well compacted non-
plastic granular infill material. The tensile strength
of the perforated HDPE geocells is observed as
12 MPa by testing 150 mm of high geocells by
loading across the full height. The geocell elements
have a characteristic depth and an effective
diameter which is a function of the weld spacing.
Hence, in finite element or finite difference
numerical analyses it is possible to model the
geocell layer as a three-dimensional structure with
interconnected cells. In these models, the geocell
walls are modelled as membrane elements
connected at the weld locations. However, in
simple
hand calculations or limit equilibrium analyses, the
geocell layer is included as explained below.
67.5 The soil infilled in the geocell pockets exhibit
“apparent cohesion” due to confinement within the
cells, besides the angle of internal friction of the
compacted non-plastic material. “Apparent
cohesion” has been derived by Bathurst and
Rajagopal (1993) and confirmed by laboratory tests
that a geocell layer infilled with non-plastic soil can
be considered as a stratum with an equivalent
cohesive strength (besides its friction angle φ),
which is derived by virtue of confinement of the soil
by the geocell walls. The strength of the geocell-
infill system is best explained by the Mohr-
Coulomb failure envelop in Fig. 87. The figure
illustrates the effect of confining pressure within the
cell, ∆σ3 on the confined soil to generate a higher
shear strength (larger circle), whose parallel tangent
intercept is at cτ on the shear stress axis; cτ is called
“apparent cohesion” as the soil is basically
cohesionless granular soil. The slope of the tangent
of the larger circle is the angle of internal friction φ
which is found to be unaffected by the geocell
confinement.
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FIG. 87 EFFECT OF CELL CONFINEMENT ON NON-PLASTIC SOIL — “APPARENT COHESION” AND FRICTION
ANGLE
From Fig. 87, the apparent cohesion could be
related to the confining pressure and soil properties
as:
M is the secant modulus of the geocell straps
( 350 kN/m at 2 percent strain for perforated
HDPE geocells), d is the equivalent pocket opening
diameter ( 0.23 m). a is the allowable axial strain
of the infill material (may be taken as about
1 percent to 2 percent). Substituting these values
with a = 2 percent, the additional confining
pressure comes to 31 kPa and apparent cohesion c
comes to about 27 kPa. At 1 percent axial strain the
apparent cohesion comes to 13.5 kPa. Hence,
typical apparent cohesion values for an infill soil
having 30 friction angle may be taken as 15 kPa
for an HDPE geocell.
67.6 Analysis
67.6.1 When the geocells infilled with non-plastic
soil are used as basal mattresses, the geocell layer
contributes to the load support in two ways, one by
imparting apparent cohesion to the infill soil and the
other by tensile resistance developed in the plane of
the geocell layer. The geocell layer is treated as an
equivalent soil layer having the height of geocell and
having the properties of apparent cohesion and
friction angle of infill soil.
The in plane tensile force per unit length due to the
geocell layer can be estimated as:
Where 12 is the tensile strength of the HDPE
material in MPa units, the factor 0.85 is to account
for the inclination of geocell straps over some
length, n is the number of straps within a unit
length of the section (typically 4 to 5 depending on
the weld distance) h is the height of the geocell
layer in m and t is the thickness of the geocell walls
in mm. The tensile force may be applied at mid-
height of the geocell layer. The factor RF is a
reduction factor to consider the installation
damage, creep and other environmental factors as
per 64.13. The value of this factor depends on the
gradation of the infill material, method of
compaction, required service life, etc. In general,
the requirement of geocell as a basal layer will go
on reducing with time as the subgrade soil gains in
strength. Within a few years after construction, the
subgrade may gain adequate strength that the basal
geocell mattress may not actually be required for
the stability of the system. Based on these
considerations, the value of the reduction factor RF
may be selected.
IS 18591 : 2024
143
𝑐𝜏 =
∆ 𝜎3
2
∗ √𝐾𝑝 …(8.23)
In which ∆𝜎3is the additional confining pressure
developed in the soil due to membrane action of the
geocell pockets. The additional confining pressure
could be estimated as:
∆𝜎3 =
2.𝑀
𝑑
(1−√1−𝜖𝑎)
(1−𝜀𝑎)
…(8.24)
T = 0.85  12  n  h  t/RF kN/m …(8.25)
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67.6.2 Conventional slope stability analysis
software such as ReSSA (reinforced slope stability
analysis) may be used to determine the safety
factors as per 64.8 and 64.11. The geocell layer is
replaced with an equivalent soil layer of this height
and having apparent cohesive strength and
frictional strength. The tensile force contribution
due to geocell membrane action is considered as a
horizontal reinforcement force at mid-height of this
equivalent soil layer.
68 STABILITY IN THE DIRECTION ALONG
THE EMBANKMENT
The differential fill height along the embankment
should be limited to a minimum during construction
of the embankment, but there will inevitably be a
need for the basal reinforcement to provide some
degree of stability in the longitudinal direction and
at the ends of the embankment. The reinforcement
force needed should be determined taking account
of the likely differential fill heights during
construction.
69 ALLOWABLE STRAIN IN
REINFORCEMENT
Maximum strain in the reinforcement should not
exceed 5 percent for short term application and
5 percent to 10 percent for long term application.
Embankment on sensitive soil like peat the
maximum strain in the reinforcement for short term
shall not exceed 3 percent.
70 MULTIPLE REINFORCEMENT BASAL
LAYERS
70.1 The maximum limit state tensile force to be
resisted by the basal reinforcement could
theoretically be provided by two or more multiple
reinforcement layers installed at the base of the
proposed embankment.
70.2 However, observations of field trials
(see Rowe and Li, 1993) have indicated that where
settlements are relatively large ( H/25) and varying
strength reinforcement materials have been installed
in basally reinforced embankments, the stronger
reinforcement attracts a disproportionately higher
level of the mobilized resisting force. Similarly,
when two identical strength layers are incorporated
as basal reinforcement, the lowest layer attracts
a higher proportion of the resisting force
(see Blume et al., 2006).
70.3 The precise distribution of forces it not fully
understood; it is therefore recommended that, where
possible, the maximum limit state tensile force
should be provided in one reinforcement layer.
Where this is not possible then consideration should
be given to the use of multiple layers of equal
strength and stiffness to provide design tensile
reinforcement in each layer equivalent to:
where
TD = design strength of the reinforcement;
Ω = a coefficient dependent on the sequence of
the reinforcement layer;
for the first/lowest layer Ω = 1;
second reinforcement layer Ω ≤ 1; and
any subsequent reinforcement layers, Ω ≤ 0.5.
71 FOUNDATION SETTLEMENT
71.1 The presence of basal reinforcement alone does
not influence the settlement characteristics of the
embankment; thus, settlement analyses may be
performed using conventional procedures.
71.2 Foundation settlement may be assumed to
increase the tensile strain and hence load, in the
reinforcement. Intermediate and long-term
settlements may be expected to offset any reduction
in reinforcement load due to an increase in
embankment stability.
71.3 Settlement of embankments and more
importantly, rate of settlement consideration are of
relevance because such settlements will affect the
performance of structure, especially in terms of
developing uneven surface on top. By providing
reinforcement at the base of the embankment will
leads to partial improvement in the differential
settlement because of the relatively uniform
distribution of the stress on the foundation layer.
71.4 Subsoil layers experience settlement due to
embankment loads the magnitude and time rate at
which these settlements progress depends on the
nature of the subsoil:
a) Where subsoil layers are essentially low
plastic or non-plastic soils, with adequate
bearing capacity, settlements in the subsoil
progress as the embankment is built up.
Thus, there would be none or very small
post-construction settlements at the end of
construction. Hence, such settlements are
not of concern; and
b) Where the subsoil consists of soft
compressible clay layers in saturated
condition, large settlements would occur.
These settlements follow the “Terzaghi’s
theory of consolidation” and require long
time-period for completion. It is essential
that such subsoil conditions are identified
at or prior to design stage and suitable
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𝑇𝐷 ≥ 𝛺𝑇1 + 𝛺𝑇2 … … … + 𝛺𝑇𝑛 …(8.26)
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ground improvement technique is adopted.
Such techniques accelerate the settlement
rate based on the design adopted. However
even at the end of the waiting period after
ground improvement method adopted,
some settlements may continue to occur.
These may be termed “post-construction
settlements”.
71.5 The allowable limit for such post-construction
settlement may be considered as 300 mm for
embankment supporting roads. The allowable limit
may be decided based on agreement between
designer and owner of the project. In general, these
settlements progress at very slow rate. Hence it
would be economical to allow such settlements to
run their course than aim a design which has
“negligible” post-construction settlements. This
observation is particularly relevant where PVDs or
stone columns are adopted for ground improvement.
The designer may indicate the amount of
post-construction settlement expected and time
period for the same while designing embankments
over soft subsoil deposits. In case of embankments
on soft clays, where post-construction settlements as
mentioned above are difficult to avoid, rigid
pavements or rigid structures may not be suitable.
72 BASAL REINFORCED EMBANKMENTS
WITH VERTICAL DRAINS
72.1 Technical as well as economic benefits may be
gained in accelerating the rate of consolidation
(and hence the rate of shear strength increase) of soft
foundation soils. For example, a higher load level in
the reinforcement may be utilized if the time over
which the reinforcement force is needed is reduced.
72.2 Several methods of accelerating consolidation
may be used, including the use of surcharge, vacuum
preloading, and vertical drains. The technique using
vertical drains is shown in Fig. 87.
72.3 Ideally, the reinforcement should be placed
after the vertical drains have been installed as
damage to the reinforcement due to drain installation
is avoided.
SECTION 9
DRAINAGE DETAILING
73 INTRODUCTION
73.1 This section provides general recommendations
for incorporating drainage elements (surface and
subsurface) for reinforced soil structures. This
section covers several site situations that require
drainage and how to combine them into a reinforced
soil structure. Components of subsections include:
a) External drainage:
1) Surface drainage;
2) Slope end for bridge approaches; and
3) At the toe.
b) Internal drainage:
1) Backfill;
2) Interface between backfill and
reinforced soil; and
3) Body of reinforced soil component of
the structure:
i) Transverse through the
ii) Along the fascia; and
iii) At the base.
73.2 To describe long term drainage measures, the
groundwater research should include information on
the permeability of the fill or ground to be reinforced
as well as the underlying strata.
73.3 It is possible to minimize hydrostatic stresses in
geosynthetic reinforced soil retaining structures by
constructing internal and external drainage systems
and considering drainage aspect listed below:
a) Potential for pore water pressure buildup
inside the reinforced structure (stability);
b) Potential for buildup of harmful elements
within the reinforced zone (durability);
and
c) Characteristics of consolidation
(settlement/serviceability).
Stability, durability, and serviceability are all
aspects of drainage design that designers should be
aware of while designing reinforced soil structure.
They must also determine if any relevant standards
applicable to their project.
74 SITE CONDITIONS REQUIRING
DRAINAGE
Several conditions exist at site that needs the
inclusion of one or more drainage measures are
required to reduce or eliminate hydrostatic forces in
a reinforced soil retaining structure:
a) Surface water flowing towards the
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reinforced soil retaining structure;
b) Catch basins/drop structures inside a
reinforced soil retention structure;
c) Heavy precipitation;
d) Rise in ground water table;
e) Drainage structures for outlets through
retaining structure faces; and
f) Top and/or toe of the drainage pipes.
74.1 Surface Water Flowing Towards the
Reinforced Soil Retaining Structure
74.1.1 Site drainage should direct surface water
away from the geosynthetic reinforced soil retaining
structure (reinforced soil structure) by using an edge
drainage provisions similar to a curb and drain.
Extreme weather can damage reinforced soil
retaining structures (that is, thunderstorms). Hence,
in such cases site civil engineer should develop the
runoff pattern in coordination with the reinforced
soil structure designer.
74.1.2 It is challenging to develop features for a
specific or enforced design storm. Many storm water
management solutions are based on 100 year storms.
Designer must follow recommendations provided in
Section 4 for the storm water conditions and
waterfront structures and shall adhere to the
relevant material specification as illustrated in
Section 3.
74.1.3 A reinforced soil structure designer must
work with other project authorities to address excess
flows. Overflow (for example, spillways) elements
should be addressed in the design of reinforced soil
walls where surface water flows toward the wall.
74.1.4 General guidance is indicated in the Fig. 88
and Fig. 89 for the full height reinforced soil
structure and partially high reinforced soil structure.
FIG. 88 TYPICAL DRAINAGE DETAILING FOR FULL HEIGHT GEOSYNTHETIC REINFORCED SOIL
RETAINING STRUCTURE EDGE (TYPICAL PANEL FASCIA — DRAWING NOT TO SCALE)
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FIG. 89 TYPICAL DRAINAGE DETAILING FOR PARTIALLY HIGH GEOSYNTHETIC REINFORCED SOIL
RETAINING STRUCTURE EDGE (TYPICAL FACING PANEL)
74.2 Catch Basins/Drop Inlet Structures Inside a
Reinforced Soil Retention Structure
The reinforced soil mass should be situated outside
catch basins, drop inlet structures and storm drain
lines wherever practical. Soil erosion has caused
many reinforced soil retaining structures to collapse.
These constructions aggravate soil erosion
(that is, soil to be washed into the structures through
poorly constructed joints or when settlement occurs
causing openings between inlet structures and
discharge pipes to occur). Special care must be used
when constructing soil reinforcement around
structures such as catch basins and manholes
[see Fig. 90 and Fig. 91 for typical detailing].
74.3 Fine Grained Soil Used for the Reinforced
Fill
74.3.1 Many parts of the country lack granular soils
for use as reinforced fill. Some areas of the country
have fine-grained soils ( 50 percent). When using
fine-grained soils (infill), reinforced soil structure
should not migrate unsatisfactorily over time.
Internal and exterior drainage are distinct. Using
internal drainage features such drainage aggregate,
geotextile filter, drain-pipe and blanket drain is
recommended when working with fine grain
soils. Please refer to Section 3 for general
recommendation on reinforced fill material
specifications and related standards.
74.3.2 When fine-grained soil is used to construct
reinforced soil walls/slopes, stress cracks frequently
form between the reinforced and retained soil. This
occurs as the wall settles. It ties the reinforced soil
material together. Stress cracks emerge in the rein
forced soil mass when it settles (Fig. 92). Entrapped
water raises hydrostatic pressure behind the
reinforced soil mass.
74.3.3 A provision of chimney drain or composite
drain constructed behind the reinforced soil mass
would allow water entering the stress crack to
escape. Phenomenon of water infiltration is most
prevalent in hilly terrain. Fig. 93 and Fig. 94 shows
detailing of typical trench drain for medium and
high-water flow intensity in areas of cutting.
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FIG. 90 SECTION WITH STORM WATER LINE PENETRATING REINFORCED SOIL RETAINING STRUCTURE
FACE (TYPICAL PRECAST CONCRETE BLOCK FASCIA)
FIG. 91 ELEVATION VIEW OF STORMWATER LINE PENETRATION (TYPICAL PRECAST CONCRETE BLOCK
FASCIA)
FIG. 92 TENSION CRACK THAT MAY DEVELOP WHEN FINE GRAINED SOILS ARE USED AS REINFORCED
AND RETAINED SOIL (TYPICAL PRECAST CONCRETE BLOCK FASCIA)
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FIG. 93 PROVISION OF TRENCH DRAIN IN HILLY AREAS WITH MEDIUM RAINFALL INTENSITY
FIG. 94 PROVISION OF TRENCH DRAIN IN HILLY AREAS WITH HIGH RAINFALL INTENSITY
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74.4 Snow Melt Saturation and Strong
Precipitation
In the north and north-eastern states of Himalayan
belt, snow melt may cause the slow saturation of the
reinforced and retained soil behind a reinforced soil
structure. If the soils used to construct the wall
have a high percentage of fine-grained particles
(that is, greater than 35 percent), the soil behaves as
a fine-grained soil. The slow melting of the snow can
saturate these soils. If internal drainage is not
included the soils may become saturated. The result
is a loss in shear strength, an increase in driving
force and a potential failure of the reinforced soil
structure.
74.5 Rise in Ground Water Table
As mentioned before, the usage of an internal
drainage system is required in high groundwater
circumstances. A blanket drain should be installed if
the groundwater table is projected to rise to the
bottom of the wall. A drainage blanket and chimney
drain shall be considered if the groundwater table is
projected to rise over the levelling pad during the life
of the construction. It may not be practicable to
avoid hydrostatic forces when designing for high
groundwater conditions. In the design of the
reinforced soil structure, following sub-section offer
guidelines on how the hydrostatic forces are handled
while designing the reinforced soil structure.
74.6 Drainage Structures for Outlets Through
Retaining Structure Face
Larger diameter outlet pipes should not pierce the
wall fascia (pipe diameter more than 150 mm).
Storm water management structures have the
capacity to transport huge amounts of water at high
speeds through wall face penetrations. Erosion at the
toe of the wall, as well as movement of drainage
stone and/or reinforced fill via the connection
between the outlet pipe and reinforced soil structure
units, are just a few of the consequences.
Next section contains information on how to avoid
these issues.
74.7 Slope at the Top and/or Toe of the
Reinforced Soil Structure
74.7.1 A slope at the top or bottom of reinforced soil
structure is vulnerable to erosion by surface water.
The possibility for erosion should be considered
while designing the wall and suitable
erosion control techniques should be included
(see subsequent section).
74.7.2 The points listed above are not an exhaustive
list of circumstances that necessitate drainage
features or considerations. This list is mainly
intended to emphasize the importance of drainage
elements in a reinforced soil structure. Drainage
elements should be carefully considered so that
hydrostatic forces do not effect on the reinforced soil
structure. However, if this is not possible, the
reinforced soil structure must be designed to account
for these hydrostatic forces. The analytical methods
necessary to evaluate the performance of the
reinforced soil structure when hydrostatic forces are
present will be presented in subsequent section.
FIG. 95 TENSION CRACK THAT MAY DEVELOP WHEN FINE GRAINED SOILS ARE USED AS REINFORCED
AND RETAINED SOIL (TYPICAL PRECAST CONCRETE BLOCK FASCIA)
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75 OVERVIEW OF REINFORCED SOIL
RETAINING STRUCTURE DRAINAGE
FEATURES
It is necessary for RS wall to have sufficient
drainage in order for it to function properly. There
are two types of drainage considerations for
RS wall: internal and external. One of the internal
drainage difficulties is preventing surface or
subgrade water from infiltrating the reinforced soil
mass. Internal drainage is determined by the
reinforced fill's properties. External drainage issues
involve external water pouring over and/or around
the wall surface, putting a strain on the internal
drainage system and/or producing external erosion.
The positioning of the RS Wall in respect to local
hydrogeological conditions determines external
drainage, which is concerned with channeling water
away from the soil structure.
75.1 Drainage Aggregates
75.1.1 Engineered drainage aggregate (Fig. 96) is
an essential component of a well-designed
reinforced soil structure. Open graded gravel is
commonly used as drainage aggregate (that is, GP).
In many cases, a geotextile layer separates the
drainage aggregate from the reinforced fill soils and
contains a drainage pipe to direct accumulated
water away from the structure. The drainage
aggregate placed behind reinforced soil structure
solid block units must be at least 300 mm thick. A
well-designed drainage aggregate system installed
right behind the
reinforced soil structure block units will accomplish
the following:
a) Prevent hydrostatic pressure from building
up at the wall's face, in the retained
(reinforced) soils, and in the foundation
soils near the wall's toe; and
b) Provides a supplementary benefit by
facilitating compaction of fill directly
behind block units, preventing residual
soils from washing through the face of the
wall.
Fig. 96 demonstrates the significance of filter
media as a transition zone for reinforcement
between concrete fascia and flexible compacted soil
in order to lessen the likelihood of rupture at the
transition zone while also functioning as drainage
for ingress water.
75.1.2 Unless the engineer determines that such
measures are not required for a specific project, it is
advised that suitable drainage features be supplied
for all walls. The engineer must consider both
subsurface and surface infiltration water when
determining the necessity for drainage measures.
75.1.3 A well-designed drainage feature takes into
account the filtering properties of various
geomaterials both inside and outside the reinforced
soil wall, as well as drains that are appropriately
proportioned to properly remove any seepage
water. Fig. 97 shows the potential sources and flow
paths of water.
FIG. 96 DRAINAGE FEATURES FOR CONSIDERATION WHEN WATER IS PRESENT IN REINFORCED SOIL
STRUCTURE (TYPICAL PRECAST CONCRETE BLOCK FASCIA)
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FIG. 97 POTENTIAL SOURCES AND FLOW PATHS OF WATER
75.2 Internal Drainage Systems
75.2.1 There are two specific forms of internal
drainage:
a) Drainage near wall face due to infiltration of
surface water near the wall fascia; and
b) Drainage behind and under reinforced soil
zone from ground water.
75.2.2 A groundwater surface beneath reinforced
soil structure may rise into the reinforced soil mass,
depending on the hydrogeology of the site. Surface
water may infiltrate into the reinforced soil mass
from above or from the front face of the wall, for the
case of flowing water in front of the structure.
75.2.3 Internal Drainage Near Wall Fascia
A filter is provided at all vertical and horizontal
joints in the wall face to restrict the movement of
fines through the joints from the reinforced soil mass
through the joints.
For precast concrete segmental wall facing, the filter
is commonly in the form of nonwoven geotextile.
The placement of geotextile is shown in Fig. 98.
The geotextile filter should extend a minimum of
100 mm on either side of the joint and additionally
up into the coping to prevent soil from moving
around and bypassing the geotextile filter.
NOTE — Strips of filter cloth shall be placed on back
face of panel, over panel joints. filter cloth shall be
adhered to back face of panels using an non-water
soluble adhesive
Modular block wall facing units are typically
constructed with a zone of free drainage aggregates
adjacent at the back face of the units. This aggregate
zone is also required for stiffness of the wall face and
constructability apart from serving as a back face
drain (refer Fig. 96 for details).
Fig. 99 illustrates a typical drainage detail for wire-
faced reinforced structures. The geotextile filter is
positioned between the facing stones and the
reinforced soil mass.
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FIG. 98 EXAMPLE LAYOUT OF GEOTEXTILE FILTER AT JOINTS BETWEEN SEGMENTAL PRECAST CONCRETE
PANEL FACING UNITS
FIG. 99 EXAMPLE LAYOUT OF GEOTEXTILE FILTER NEAR THE FACE FOR WELDED WIRE FASCIA
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FIG. 100 ENLARGED CROSS SECTIONAL VIEW OF THE WELDED WIRE MESH (DETAIL A)
Fig. 101 illustrates a typical drainage detail for geocell fascia reinforced soil structures.
FIG. 101 EXAMPLE LAYOUT OF FILTER NEAR THE FACE FOR GEOCELL FASCIA REINFORCED SOIL STRUCTURE
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FIG. 102 SCHEMATIC OF FILTER GEOTEXTILE BEHIND GABION FACING
75.2.4 Internal Drainage Under and Behind the
Reinforced Soil Wall
For walls located in areas where groundwater can
produce a build-up of seepage forces within the
height of the reinforced soil mass, it is advised to
install a base drain beneath the reinforced soil
structure and a rear or chimney drain behind
the reinforced zone to assure the reinforced soil
structure's long-term design.
Fig. 103 to Fig. 106 illustrate a base and back
drainage system for a segmental precast panel and
block fascia structures. In Fig. 107 to Fig. 110,
blanket drains and geo-composite drains are shown
in place of open graded gravel drains with a
geotextile or properly graded soil filter.
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FIG. 103 SCHEMATIC OF DRAINAGE BLANKET BEHIND THE RETAINED FILL
(TYPICAL CONCRETE PANEL FACED WALL)
FIG. 104 EXAMPLE DRAINAGE BLANKET BEHIND THE RETAINED BACKFILL USING GEOCOMPOSITE AND
DRAINAGE AGGREGATES
(TYPICAL CONCRETE PANEL FASCIA)
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FIG. 105 EXAMPLE DRAINAGE BLANKET BEHIND THE RETAINED BACKFILL USING DRAINAGE AGGREGATES
(TYPICAL BLOCK FASCIA)
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FIG. 106 SCHEMATIC OF DRAINAGE MEASURES FOR PARTIAL REINFORCED SOIL WALL
(TYPICAL BLOCK FASCIA — DIMENSIONS ON THE DRAWING ARE FOR ILLUSTRATIVE PURPOSE ONLY)
FIG. 107 EXAMPLE DRAINAGE DETAIL USING A BLANKET DRAIN WITH CHIMNEY DRAIN
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FIG. 108 EXAMPLE DRAINAGE DETAIL USING GEOCOMPOSITE DRAIN
(TYPICAL CONCRETE FASCIA)
FIG. 109 EXAMPLE DRAINAGE DETAIL USING
GEOCOMPOSITE DRAIN — SPACING
FIG. 110 EXAMPLE DRAINAGE DETAIL USING
GEOCOMPOSITE DRAIN
Fig. 111 shows the typical arrangement of geocomposite behind reinforced soil structure using block fascia
where filter media is not available. Fig. 112 illustrates gravel media only at the junction of two consecutive
block units. Fig. 113 depicts gravel media and geo-composite behind reinforced soil structure using block fascia.
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FIG. 111 EXAMPLE DRAINAGE DETAILING USING GEOCOMPOSITE BEHIND PRECAST CONCRETE BLOCK FASCIA
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FIG. 112 EXAMPLE DRAINAGE DETAILING USING
GEOCOMPOSITE BEHIND PRECAST CONCRETE BLOCK
FASCIA (PROVISION OF FILTER MEDIA AT JUNCTION
OF ADJACENT BLOCK)
FIG. 113 EXAMPLE DRAINAGE DETAILING USING
GEOCOMPOSITE AND FILTER MEDIA BEHIND
PRECAST CONCRETE BLOCK FASCIA
NOTE — The geocomposite must be properly covered and bonded so that soil cannot enter the geocomposite.
75.3 External Drainage
Surface drainage is critical for ensuring the
performance of reinforced soil walls, and adequate
techniques to minimize surface water infiltration
into the wall backfill should be incorporated into the
design.
During the construction of a reinforced soil wall, the
contractor should grade the wall fill surface away
from the wall face at the end of each day to prevent
water from ponding behind the wall and saturating
the soil. Along with softening the subgrade, surface
water flowing onto a partially completed wall fill
can transport fines into the backfill work area,
contaminating a free-draining granular backfill on a
local level. Saturation might result in displacement
of the partially completed wall if finer grained
backfill is used for reinforced wall fill. When
possible, final grading at the top of a wall
construction should direct drainage away from the
wall to prevent or limit surface water infiltration into
the reinforced wall fill.
Collection and conveyance swales should prevent
overtopping of the wall for the design storm event.
Extreme events such as brief periods of high rainfall
have been known to inflict significant damage to soil
retaining structures through erosion and
undermining, floods, and/or increased hydrostatic
pressures both during and after construction. This is
especially true for locations with surface drainage
directed toward the wall construction and coarse
grained backfill.
If surface water is likely to flow toward the structure,
it should be collected in a gutter or other collecting
feature that is part of the site drainage system and is
planned for an assumed or prescribed design storm
event. For reinforced earth walls, the storm event
should be at least 100 years in duration. However,
extreme occurrences might result in short duration
flows, for example, 1 h to 3 h, that greatly exceed
the storm water management system's design
capacity. When such events occur, they can result in
the wall collapsing, erosion and undermining, as
well as an increase in hydrostatic forces within and
behind the reinforced soil mass. As a result, wall
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structure should incorporate additional drainage
media for handling flows bigger than the design
storm event. It is necessary the site engineer should
consider potential overflows and coordinate work
with the RS wall designer for drainage detailing.
75.4 Peripheral Drains at Top of Wall
75.4.1 Peripheral drain at the top of geosynthetics
reinforced soil structure shall be provided to divert
the surface runoff in a controlled manner to an
outlet. It helps in reducing the potential for surface
water from overtopping the wall. Fig. 114 to
Fig. 116 show typical drainage details for precast
concrete panel facing and modular block wall units.
The project engineer and the RS wall designer
should address and detail the outlet for the peripheral
drain if it is used. For example, the peripheral drain
can be detailed to discharge water at the end of the
wall structure or to low overflow points along the
wall length. The designer should anticipate and
address in design and detailing the possibility of
water runoff from extreme events which will
overtop the drainage peripheral drain and run down
the wall face, unless the peripheral drains are
specifically sized for such events. For sloping
backfills, wall designer should also address
collection and diversion of water at the top of the
slope. Site water runoff from above the back slope
should not be directed toward the reinforced soil
wall back slope.
75.4.2 In case of vegetative peripheral drains,
shrinkage cracks in the low permeability soil during
periods of extended dry weather may increase the
permeability of the layer to the extent that it is no
longer an effective barrier layer. Therefore, a
geomembrane ghould be used beneath any
vegetative peripheral drain.
FIG. 114 DRAINAGE DETAILING NEAR TOP EDGE OF THE WALL
FIG. 115 DRAINAGE DETAILING AT TOP EDGE
OF THE RS WALL (PRECAST CONCRETE BLOCKS)
FIG. 116 DRAINAGE DETAILING AT TOP EDGE OF
THE RS WALL (PRECAST CONCRETE BLOCKS)
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75.5 Geomembrane Barriers
A geomembrane barrier can be used to prevent
surface water infiltration and associated seepage
forces that can occur when using poorly draining
reinforced fill. The geomembrane barrier should be
placed below the road base and just above the first
layer of soil reinforcement. The geomembrane
should be tied into a drainage system to collect and
discharge the runoff.
An example detail for use of geomembrane barrier
to prevent infiltration of runoff into the reinforced
soil mass is illustrated in Fig. 117. As shown in
Fig. 117, the geomembrane should be sloped to
drain away from the facing to an intercepting
infiltration barrier.
75.6 Pavement Permeability and Runoff
75.6.1 Surface water flows through asphalt
pavement cracks and concrete joints and cracks into
the pavement base materials. The flow into the base
aggregates can be significant, with up to 50 percent
of the water falling on the pavement, then to the base
course and much more if there are cracks present in
the pavement. This inflow of water saturates the
subgrade because the relatively high permeability
base aggregate ponds the water above the reinforced
soil wall. The project civil engineer to ensure that
such a condition is mitigated, and positive drainage
measures are provided to capture the pavement
drainage in the form of proper grading away from
the wall and edge drains. Proper attention should be
given to use the geomembrane detail shown in
Fig. 106, to intercept and discharge the water
seeping through cracks in the pavement.
75.6.2 Surface runoff on the pavements that
overtops the wall can cause weakening of the wall.
Sloping of roadway towards a ditch is a common
way to guard against wall overtopping. This is also
sometimes referred to as roadway ‘in sloping’.
FIG. 117 EXAMPLE GEOMEMBRANE BARRIER DETAILS (TYPICAL CONCRETE PANEL FASCIA)
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75.7 Grade at Ends of the Reinforced Soil
Structure
75.7.1 The final grade at the toe and ends of the
reinforced soil structure, both as designed and as
constructed, is an important consideration for water
flow conditions. Surface water flow along the toe
may occur around the ends or along the face of the
structure and has the potential to erode the soil. This
erosion eventually may weaken the facing units of
reinforced soil structure. Proper site grading and
with a soil berm or slope at the toe of the wall can
direct the flow away from the toe of wall structures.
75.7.2 Erosion control details are required where
water will flow adjacent to the wall face. Geotextile
lined riprap stone or other means should be used to
prevent scour. The designer also may elect to embed
the wall deeper where there is potential for erosion
of the wall toe. Consideration should be given to
turning the wall 90 degrees inward from the face.
75.7.3 The ends of the wall that terminate in or
intercept embankment slopes should also be
protected from erosion. Walls that terminate in
slopes should be adequately keyed into the slope and
a peripheral drain used to divert water away from the
ends of the wall to mitigate erosion. Wing walls for
approach fills should also be design such that water
does not flow down the slope along the back of the
wall face. Again, a peripheral drain can be used to
divert water and the surface of the slope should be
graded to promote water flows away from the wall.
75.8 Toe End Protection of the Reinforced Soil
Structure
For the protection of the water at tail end several
measures are required. Listed below are few of
them:
a) Embedment of RS structure
Water can scour the structure subgrade if
there is no embedment or if the fill is not
sufficiently compacted. Failure may cause
at the embedment portion of the reinforced
soil structure due to negligence of the
compaction. As a preventative measure
Fig. 118 depicts the highlighted area of the
embedment with adequate compaction.
b) Tail end protection
Toe embedment shall be at least 1 m below
the service road/completed ground level.
Also, for effective toe protection, hard
topping/plinth protection is required. Tail
end protection is essential during
construction of reinforced soil structure,
especially during the monsoon season,
proper water routing is critical. Tail end
protection that is well compacted can help
to prevent failures.
c) Pipe encasement
To route the water, a minimum 100 mm
thick PCC encasement surrounding the
embedded pipes must be installed, with
encasement covering the complete wall
width.
FIG. 118 EMBEDMENT ZONE ENSURING ADEQUATE COMPACTION TO MINIMISE THE WATER INFILTRATION OF THE
REINFORCED SOIL STRUCTURE
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75.9 Drainage within Pavement Surface
Pavement surfaces are prone to leak. Surface water
seeps into the pavement foundation materials
through asphalt pavement fractures, concrete joints,
and cracks. The flow into the base aggregates can be
substantial, with up to 50 percent of the water that
falls on the pavement making its way to the base
course. If the subgrade soils are extremely
permeable, water may percolate through them.
If not and the site and pavement slope toward the
low spot where a reinforced soil structure supports
the fill dirt, this water flows toward the reinforced
soil structure, as indicated in Fig. 119. Due care
must be taken in such cases by providing a
peripheral drain or any other appropriate measures.
75.10 Drainage Considerations of Shored
Reinforced Soil Wall
75.10.1 As shored reinforced soil wall system is
designed for long term performance; it must
incorporate wall drainage systems for both the
shoring wall and the RS wall components. In any
case, the shoring component's drainage should be
connected to the RS component's drainage system.
Considering that SRS walls' reinforced fill zone is
described as a freely draining granular material,
drainage behind the reinforced fill zone is optional.
Drainage should be included directly beneath the
wall face when using modular block units or
another semi-permeable facing material. Fig. 120
shows an SRS wall (a soil nail shoring wall) with
internal drainage that exits through the RS
component. Fig. 120 shows semi-perforated
drainage pipe and a drainage blanket installed
behind and beneath the reinforced fill zone in areas
with high groundwater levels.
75.10.2 Surface water infiltration should be kept to
a minimum in an SRS wall system. This is especially
critical for deicing chemicals used on roadways, as
they might degrade steel reinforcements or
connectors. For RS components with metallic
reinforcements that support chemically deiced
highways, an impervious geomembrane should be
installed beneath the pavement and above the first
row of reinforcements to intercept aggressive
chemical-laden flow.
75.11 Drainage Detailing for Tiered Structure
For tiered reinforced soil wall system, drainage
outlets are required to provide at each berm to
minimize the development of seepage pressure
within the reinforced zone Fig. 121 to Fig. 123
shows the typical details of the drainage
arrangement for the tiered wall structure.
FIG. 119 WATER FLOW INTO REINFORCED SOIL STRUCTURE THROUGH BASE COURSE DUE TO
CRACKS IN PAVEMENT
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FIG. 120 EXAMPLE DRAINAGE CONSIDERATIONS FOR AN SRS WALL SYSTEM
(TYPICAL CONCRETE PANEL FASCIA)
FIG. 121 DRAINAGE CONSIDERATIONS FOR A TIERED WALL
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FIG. 122 TYPICAL DETAILING OF A TIERED WALL (DETAILING AT BERM)
FIG. 123 DRAINAGE DETAILING FOR A TIERED WALL (TYPICAL PANEL FASCIA)
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76 MONSOON PREPARATION AND
PLANNING
Specific measures must be taken to avoid water
ponding over the RS system. It is also necessary to
prevent rain cuts through adequate protective
measures grading backfill to appropriate slopes to
direct runoff. At the toe, compacted fill with firm
topping will be provided. The plinth protection at the
toe will be slanted outwards toward the service road.
Always plan ahead of time for monsoons to avoid
building complications during the rains. Fig. 124
shows typical outline for the drainage preparation
during monsoon.
77 MAINTENANCE OF DRAINAGE
77.1 Features that minimize water flow and preserve
reinforced soil structure drainage should be
maintained over the life of the structure. For
example, cracks in pavement above reinforced soil
structure should be sealed. Differential settlements
and pavement cracks around catch basins should be
such that there is minimum potential inflow into the
reinforced soil or retained soil mass. Screens should
be installed on drainage pipe outlets to prevent the
clogging of pipes. Outlet screens and cleanouts to
provide access to clogged drainage should be
detailed on the retaining wall construction drawings.
77.2 Outlets in soil embankments should drain onto
a concrete apron and should be marked with a
permanent metal fence post. This minimize the
chance of the outlet being run over and crushed by
mowers or covered in subsequent construction
activities. This should be detained on the wall
construction drawings.
FIG. 124 PROVISION OF SLOPE GRADIENTS TO ROUTE WATER AND PREVENT PONDING DURING THE MONSOON
SEASON
SECTION 10
DETAILING AND CONSTRUCTION ASPECTS
78 SCOPE
This section deals with the detailing of design and
construction aspects of “reinforced soil wall
systems” for various reinforced soil applications
covered by this code.
79 DESIGN DETAILING
The design output shall contain the required
geometry of the structure to be built, relevant
specification of materials or products assumed in the
design together with any further details such as
phasing of the works. Table 38 provides details for
such possible aspects of the design output.
79.1 Reinforced Soil Wall Top and Bottom
Elements
The top surface of the wall should be graded such
that water drains away from the wall. A grassed
swale or concrete ditch can be used behind the facing
to collect and remove water.
The primary bottom of wall element is a leveling
pad. Fig. 126 shows common details of a leveling
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pad. Some considerations for the leveling pad are as
follows:
a) The leveling pad should be constructed
with plain cement concrete. The common
thickness of the leveling pad is 150 mm and
width is such that it extends 75 mm beyond
the thickness of the facing unit. The
strength and thickness of the leveling pad
should allow cracking if needed to relieve
stress concentrations that can occur
during differential settlements. 20 mm
construction joints may be placed at every
20 m stretch length. The grade of concrete
for leveling pad shall be M15;
b) The width of the leveling pad may be
increased for precast concrete facing units
at sharp curves such that the entire panel
rests on the leveling pad and sufficient
overhang of the leveling pad is there on
each side of the facing unit;
c) The top of the leveling pad within any
given step should be such that it does not
vary by more than 3 mm over any 3 m run
for preventing misalignment of joints and
ease of construction; and
d) Gaps between the leveling pad steps should
be completely filled after erection of the
first row of panels. For openings greater
than 3 mm, unreinforced cast in place
concrete is preferred. For smaller openings,
a geotextile filter with sufficient overlap of
the panels and foundation soil could be
used to fill openings.
Table 38 Preferable Aspects of Design Output
(Clause 79)
Sl No. Detail Specifications
(1) (2) (3)
i) General Geometry including
a) Plan view
b) Typical cross sections
c) Elevation with layout
d) Details of corner and reinforcement orientation
Drainage
Construction phases
Monitoring
Level of control
Construction tolerances
Climatic condition
ii) Retained fill Physical properties:
a) Unit weight
b) Particle size distribution (Dmax, uniformity
coefficient)
c) Friction angle and cohesion at design stress levels
d) Water content
e) Water seepage susceptibility, where appropriate
iii) Reinforced
(selected) fill
Physical properties:
a) Maximum and minimum density
b) Particle size distribution, effective friction angle
and cohesion at design stress levels; plasticity
index; electrochemical, chemical and biological
properties
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Sl No. Detail Specifications
(1) (2) (3)
c) Minimum soil resistivity
d) Minimum/maximum pH
e) Maximum chloride and sulphate contents
f) Maximum organic and sulphide contents
iv) Reinforcement All types of reinforcement:
a) Type and configuration, laying direction, seams
and connections
b) Short term design strength
c) Long term design strength
d) Fill/reinforcement interaction
e) Mechanical damage related to fill particle size and
angularity
f) Structural layout
g) Installation of test samples
Steel reinforcement
a) Grade
b) Type of coating
Geosynthetic reinforcement
a) Creep behavior in accordance with applicable
standard
v) Facing and
connections
Type and shapes, aesthetic requirements
Performance
Level of facing
Performance level of reinforcement/facing connection
Specification of facing unit like: Grade of concrete, steel,
type of steel, galvanization, etc
vi) Top soil for
greened faces
Physical properties:
a) Particle size distribution
b) Contents of organic material
Chemical properties:
a) Minimum/maximum pH
Hydraulic properties:
a) Capacity of water retention
Table 38 (Concluded)
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(a) Barrier on top of panels (b) Barrier on top of Modular Block Units
FIG. 125 EXAMPLE TRAFFIC BARRIER FOR REINFORCED SOIL WALLS:
(A) BARRIER ON TOP OF PANEL FACING, (B) BARRIER ON TOP OF MODULAR BLOCK UNITS
FIG. 126 LEVELING PADS — STEP DETAIL
Steps are to be provided as per the approved
drawings prepared by technology provider.
It is advisable to protect the wall against vehicular
impact when there is a roadway immediately
adjacent to the bottom of the wall. A high curb at the
edge of the traveled roadway adjacent to the wall is
such an alternative.
79.2 Joints – Slip Joints and Butt Joints
79.2.1 Significant differential settlement may occur
at the wall face wherever the subsurface conditions
and/or wall profile change abruptly. This settlement
causes problems of joint openings and damage to
facing units. Such problems can be avoided by
providing slip joints which are continuous vertical
joints which allows the wall on each side to behave
independently. A slip joint is different than a regular
vertical joint between panels in that there is a vertical
separation between adjacent facing units that
extends the full height of the wall.
Following conditions require consideration of slip
joints, where:
a) Abrupt differential settlements of more
than 1 percent is expected;
b) There is an abrupt change in wall height of
1.5 m or more;
c) The wall is underlain by a relatively rigid
feature such as an abutment footing or rock
outcrop;
d) A light weight rigid structure such as a box
culvert intersects the face of RSW;
e) The wall terminates into a cast-in-place
structure; and
f) Tight horizontal curves occur.
79.2.2 Fig. 128 shows common slip joint details for
segmental precast concrete facing units. As shown
in the figure, the slip joint design uses either an
exposed slip joint panel having its own soil
reinforcement element or a hidden ‘backup’ panel in
the backfill behind the facing panel. In either case
the normal connection between two panels is broken
and independent movement on each side of the slip
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joint is possible. Fig. 129 shows a slip joint detail for
modular block facing walls.
79.3 Reinforcement Connections
Connections of the facing elements with the
reinforcement should be clearly defined and tested
using relevant standards. Connection test report
from the manufacturer shall be obtained. The
method statement for construction of panels and
blocks including connection details shall be
approved by approving authority. The connection
strength and layout once used in design calculations,
shall not be changed during execution, unless
approved by designer.
79.4 Corner Element and Acute Corner
79.4.1 Wall Corners
When two wall segments intersect to form an
‘external’ (for example, 90 degree) or an ‘internal’
(for example, 270 degree) corner, both wall
segments will tend to move laterally such that
corners tend to open up. Corner elements should be
provided as shown in Fig. 130 (a) and Fig. 130 (b)
to accommodate differential movements, prevent fill
from moving through the crack, and provide
aesthetic treatment. The figure is indicative. The
shape of the figure can vary with the technology
provider.
79.4.2 Acute Angle Corners
Exterior wall corners with an angle of less than
70 degrees, that is, acute angle, should be avoided
because of construction problems. However, if such
situation cannot be avoided, then the wall corner
should be based on following considerations:
a) The acute angle corner should be designed
as a bin wall for the extent of the wall
where the full length of the reinforcement
cannot be installed without considering the
opposite wall face;
b) In the bin wall section, the reinforcing
elements are either structurally connected
to wall faces forming the acute angle corner
or overlapped if there is adequate space to
develop the required pull-out strength;
c) Full-height vertical slip joints should be
provided at the interface of acute corner
and after the last column of panels where
full length reinforcement can be placed;
d) The soil reinforcement attached to the slip
joints should be oriented perpendicular to
the slip joint panels and shall be the full
design length;
e) Light weight concrete or self-compacted
fill (aggregate) should be considered as an
alternate to placing and compacting fill;
f) Deformation compatibility between the bin
wall section and the rest of the RSW
structure should be carefully evaluated; and
g) The key plan of acute corner (acute corner
length, L) is shown in Fig. 131 for self-
compacting fill material and soil
reinforcement arrangement. The backfilling
length (L’) will be governed by the acute
corner length and the area where with
equipment.
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FIG. 127 EXAMPLE SLIP JOINTS FOR SEGMENTAL PRECAST PANEL FACINGS
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FIG. 128 EXAMPLE SLIP JOINT FOR MODULAR BLOCK WALL FACINGS
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(a) (b)
FIG. 129 EXAMPLE CORNER DETAILS FOR PANELS (a) EXTERNAL CORNER
AND (b) INTERNAL CORNER
(a) (b)
FIG. 130 EXAMPLE CORNER DETAILS FOR BLOCKS (a) EXTERNAL CORNER
AND (b) INTERNAL CORNER
a) Key plan for backfill arrangement
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b) Key plan for soil reinforcement (geogrid) arrangement
FIG. 131 ACUTE CORNER DETAILS (KEY PLAN)
FIG. 132 TYPICAL CROSS SECTION OF ACUTE CORNER WALL (SECTION X-X)
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FIG. 133 TYPICAL POLYMERIC STRAP LAYOUT AND SEQUENCE FOR ACUTE CORNER
79.5 Reinforced Soil Walls with Sloping
Surcharge Treatment
79.5.1 Constant sloping surcharge not steeper than
1V : 2H slope to be maintained through-out the
RS wall stretch. For steeper slopes such as 1H : 1V,
reinforced soil slope shall be considered for the
sloping surcharge height along with suitable
surface erosion control protection measures, surface
drainage and cross drainage measures.
79.5.2 Impervious liner such as geomembrane to be
provided 100 mm below drain near top of RS wall.
79.5.3 Suitable slope protection measures such
as — coir mat with vegetation, synthetic mat with
vegetation, geocell mattress filled with aggregate,
geocell with vegetative soil cover that is followed by
a layer of nonwoven geotextile.
79.5.4 Fill material used in sloped surcharge shall
have specifications same as that of reinforced soil.
The fill shall be compacted to 97 percent of the
maximum laboratory density obtained from
modified proctor compaction test. Fill within 0.5 m
of the bottom of pavement (subgrade) shall be
compacted to a minimum of 98 percent of the
maximum dry density (MDD).
79.6 Obstructions within Reinforced Soil Mass
79.6.1 Contact between Dissimilar Metals
Several types of metallic elements such as steel
pipes and drain pipes are present in the reinforced
soil mass. Corrosion can occur when dissimilar
metals come in contact with each other due to
galvanic action. Therefore, all steel soil
reinforcements should be separated from other
metallic elements by at least 75 mm.
79.6.2 Vertical Obstructions in Reinforced Soil
Mass
79.6.2.1 Vertical obstructions are structures which
are embedded in or extend vertically through the
reinforced soil mass. Examples: Catch basin, grate
inlet, sign foundation, bridge foundation, light poles,
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guardrail post or culvert. Under no circumstances,
reinforcements should be left unconnected to the
wall face or arbitrarily cut/bent in the field to avoid
the obstructions.
79.6.2.2 A review of any modification to avoid an
obstruction must be made and approved by the
technology provider.
79.6.2.3 The best design is to adjust the location of
the obstruction and/or soil reinforcement so that
there is no interference.
79.6.3 Horizontal Obstructions in Reinforced Soil
Mass
79.6.3.1 Horizontal obstructions are structures
which are embedded in or extend horizontally
through the reinforced soil mass for a substantial
length along the wall. The horizontal obstructions
are commonly due to utilities such as storm drain
pipes. Such obstructions should be avoided as they
create construction problems and also the repairing
and maintenance of these utility pipes can be very
expensive as it may require dismantling the wall
system.
79.6.3.2 Some considerations are as follows if the
horizontal obstructions cannot be avoided:
a) For inextensible reinforcements, the
horizontal obstructions may be avoided if it
is possible to deflect the reinforcement in a
smooth manner up to 15 degrees of vertical
skew. Deflections greater than 15 degrees
tend to break the galvanization and may
reduce the tensile and pull-out resistance of
the inextensible soil reinforcements; and
b) For extensible reinforcements, the change
in orientation of the reinforcement may
increase the stress at connection and same
shall be accounted for additional
connection capacity.
79.6.3.3 It is not recommended to tie the
reinforcements to pipes. Special details must be
developed by technology provider to accommodate
the obstruction without attaching to it.
79.6.3.4 Utility pipes in the reinforced mass are
likely to settle differentially as the fill settles during
and after construction. Significant leakage of water
into reinforced soil walls can create problems
including failures. Therefore, such utilities should be
avoided.
79.6.4 Wall Face Penetrations
79.6.4.1 Pipe penetrations through the reinforced
soil and/or wall facing units maybe skew or
perpendicular angles from the wall face.
79.6.4.2 If a pipe must penetrate through the face of
the wall, the wall facing elements should be
designed to fit around the pipe such that the facing
elements are stable and the wall backfill cannot spill
through the wall face where it joins the obstruction.
79.6.4.3 Obstructions should preferably be covered
with concrete and capable enough to take the vertical
load of fill above.
79.6.4.4 For reinforced soil wall facing elements
located on such concrete surface, it will be difficult
to get adequate embedment. To ensure adequate
lateral resistance, arrangement of RCC beam may
be provided. Such one arrangement is shown in
Fig. 134 below.
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FIG. 134 BEAM AND ANCHOR ARRANGEMENT FOR REINFORCED SOIL WALLS RESTING ON
CONCRETE SURFACES
79.7 Reinforced Soil Walls in Curvature
79.7.1 Curves in walls are approximated by chords
that are equal to the nominal width of the facing
units. For precast concrete facing units, curves with
radius as small as 15 m can be achieved for 1.5 m
wide facing units with 19 mm joint opening. For
curved walls, regardless of the type of facing it is
crucial to provide details for wall layout. The
relationship of wall alignment to roadway alignment
should be clearly provided. Clear dimensions need
to be provided on project drawings for offsets from
reference alignments and whether these offsets are
relative to top of wall or bottom of wall, especially
in the event of stepped foundations.
79.7.2 Fig. 135 shows a typical detail for layout of
soil reinforcement for curved walls. Soil
reinforcements typically require 100 percent area
coverage, with block facing whereas with panel
facings reinforcements are generally discrete and
can be placed perpendicular to the wall face curves.
In the case of geosynthetic reinforcements,
excessive overlap can result in reduced pull-out
resistance since contact between geosynthetic is
smoother than contact between soil and
geosynthetic. Therefore, a minimum soil layer of
75 mm between geosynthetics in the overlap zone
is recommended as shown in Fig. 135.
79.8 Reinforced Soil Walls Near Abutment
Location
79.8.1 The foundation soil beneath the closing
reinforced soil wall being filled up during
the construction of abutment foundation
(open foundation or pile caps) shall be good quality
granular soil/sand. The treatment shall be as shown
in Fig. 136 and Fig. 137 for abutment open
foundation and pile caps respectively. Well graded
granular fill shall be placed and compacted in layers
of not more than 200 mm thickness such that no
loose soil pockets exist.
79.8.2 The closing reinforced soil wall near the
abutments shall have a minimum embedment depth
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of 1m from the finished ground level. If minimum
embedment depth is unavailable being absence of
service roads, backfilling need to be done in front of
RS wall for a depth of minimum 1 m. The backfilling
shall be done for a horizontal width of minimum
2 m and the backfill shall be suitably protected from
erosion.
79.8.3 For closing reinforced soil walls, construction
joints (slip joints) shall be provided at desired
locations based on the RS wall resting over the pile
caps to minimize differential settlements. This shall
vary on case-to-case basis based on the pile cap
details of the abutments.
FIG. 135 EXAMPLE LAYOUT OF SOIL REINFORCEMENTS FOR MODULAR BLOCK WALLS WITH CURVES
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FIG. 136 FOUNDATION TREATMENT FOR RS WALL AT OPEN FOUNDATION
FIG. 137 FOUNDATION TREATMENT FOR RS WALL NEAR PILE CAP
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79.9 Drainage Details
The drainage details for reinforced soil walls shall
be as per Section 9 drainage.
79.10 Design and Execution of Ground
Improvement
The important considerations in the planning, design
and execution of ground improvement are
summarized below:
a) Geotechnical (and where applicable
geophysical investigations) should be
carried out in accordance with Section 2 to
acquire a reliable understanding of the
ground conditions including the type,
sequence and thickness of subsurface
strata, geotechnical design parameters and
depth of ground water table and its seasonal
variations. The variability of ground
conditions should also be carefully
assessed;
b) Stability and settlement analysis should be
carried out considering all relevant details
of the reinforced soil structures and the
foundation strata. In case, it is not possible
to achieve the required factor of safeties
and/or the settlement exceeds the
permissible limits, ground improvement
will be required;
c) Options for ground improvement may be
shortlisted based on the guidelines given in
IS 13094;
d) In case additional data is required for the
detailed design of ground improvement and
for assessment of constructability,
additional investigations should be
conducted at this stage to obtain the
necessary data;
e) In the case of techniques for which BIS
codes are available, design should be
carried out in accordance with the relevant
BIS code. For techniques for which BIS
codes are not available, design may be
carried out in accordance with international
codes or guidelines or best practices;
f) All required details of ground improvement
shall be clearly shown on the construction
drawings;
g) The execution of ground improvement
should be carried out in accordance with
the approved construction drawings and
construction methodology and strictly
adhering to all quality control
requirements;
h) Wherever required, the efficacy of the
ground improvement shall be assessed by
one or more of the following:
1) Load tests;
2) In-situ tests like standard penetration
test, static cone penetration test, field
vane shear test on the improved
ground; and
3) Monitoring of settlement and pore
water pressures.
j) In the case of methods which require a
certain waiting period (between completion
of ground improvement and start of
construction of the reinforced soil
structures or between successive stages in
the construction of the reinforced soil
structure) for dissipation of excess pore
pressures, curing, strength gain etc, the
waiting periods specified in the
design/drawings shall be strictly adhered
to. If the results of monitoring or tests
show that the actual improvement achieved
during the waiting period is less than that
considered in the design, the waiting period
should be suitably increased; and
k) At sites where ground improvement is
required, the construction of the reinforced
soil structures shall start only after the
ground improvement works have been
completed including all necessary tests and
any rectification or modifications
stipulated. An exception to this could be
techniques like use of vertical drains to
accelerate the consolidation of subsurface
strata, where the reinforced soil itself is
used as a surcharge. In such cases the
construction of the reinforced soil structure
may start after the installation of vertical
drains, drainage blanket, instrumentation,
basal reinforcement (if any) and should
proceed in accordance with the approved
schedule which may be modified if
required based on the results of monitoring
of each stage.
80 CONSTRUCTION
80.1 General
80.1.1 The construction procedure of all soil
retaining structures and reinforced slopes shall
conform with the requirements which are common
to all types of reinforced fill structures, as itemized
in this section.
80.1.2 In addition, the construction procedure
should conform with the recommendations which
are specific to the relevant type of reinforced fill
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structure, as set out in the instructions provided by
the supplier of the reinforcement and of the facing
system, if applicable.
80.1.3 The construction of all reinforced fill
structures shall be executed layer-wise and in stages,
where the placing and fixing of the facing elements,
if any, and the reinforcement alternates with the
deposition, spreading, levelling and compaction of
the fill material.
80.1.4 If the reinforced fill structure has different
foundation levels construction should usually start at
the lowest foundation level.
80.2 Material Handling and Storage
80.2.1 All prefabricated facing units or palettes of
modular blocks, all batches or rolls of
reinforcements shall be identified with unambiguous
marks or labels, conforming to the denominations
used on the plans. Geosynthetic materials shall
conform to applicable standard.
80.2.2 The details of each roll or batch of
reinforcement delivered to the site shall be checked
against the materials specified and the serial
numbers shall be recorded and retained.
80.2.3 A suitable storage area of sufficient
dimensions shall be prepared to allow the unloading,
loading, storage and moving of all reinforcing and
facing materials, and accessories delivered to the
site, without damage occurring.
80.2.4 Handling and storage of reinforcing and
facing materials shall be carried out with care and in
accordance with the project specifications. The
relevant recommendations of the supplier or
technology provider should be also complied with.
80.2.5 Items having different sizes or physical
characteristics should be stacked separately.
Reinforcing and facing products take many different
forms. Where the above requirements do not apply
to a particular product, further advice may be sought
from an approving body, the supplier or the
technology provider.
80.3 Preparation of Foundation
80.3.1 Unsuitable materials shall be removed from
the area to be occupied by the reinforced fill
structure. All elements that might damage the
reinforcements shall be removed from the
foundation area. All organic matter, vegetation, slide
debris and other unstable materials shall be stripped
off and the sub-grade compacted before the placing
of any fill material. Soft spots should be removed
and replaced with well graded and compacted fill.
80.3.2 Requirements of ground improvement must
have been checked before preparing the foundation.
If any ground improvement scheme has been
proposed, it shall be satisfactorily executed first.
80.3.3 In the case of soil retaining structures with
hard facing units a trench excavation, stepped like
the foundation platform, should be provided at the
foundation level for a levelling pad beneath the
facing. This levelling pad is not a structural
foundation but temporary work to aid alignment and
facilitate the erection of the facing units. It should be
formed in-situ of thin, mass, unreinforced concrete
and rigid/unyielding foundation below the leveling
pad.
80.3.4 Mass concrete may be replaced by gravel
under thick facings such as modular blocks, sloping
panels or planter boxes. Such levelling pads are not
usually required for soft or flexible facing units.
80.4 Construction of Levelling Pad
Mark the centerline of the leveling pad on the bottom
of the trench. The centerline shall be fixed with
required offset to ensure final batter for the facing
panels specified by the technology provider.
Fix side forms for the leveling pad. Pour concrete,
compact using needle vibrators screed to the correct
level and finish using wooden floats to a flat and
smooth finish with a tolerance of ± 3 mm.
Cure for a minimum period of 48 h prior to the
commencement of panel placement.
80.5 Erection of Block/Facing Elements and
Checking Alignment
80.5.1 For all facing systems, special construction
arrangements, adequate temporary bracing systems,
such as props, wedges, clamps, steel angles etc, or
formwork shall be used for proper placement of
panels and for the safety of RS wall executing team
at site. At every stage of the construction, it shall be
ensured that any new course of facing is stable while
additional layers of backfill are placed and
compacted behind or above it before it can be
effectively held back by the reinforcements.
80.5.2 All temporary bracing systems or formwork
with the exception of lost formwork shall be
removed as soon as they are no longer necessary.
The typical bracings, clamps and wooden wedges
for panel facings are shown in Fig. 138, Fig. 139
and Fig. 140 respectively.
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80.5.3 Special construction arrangements shall be
used, at every stage of the construction, to ensure
that the final geometry is as required by the design
and within the specified tolerances. Such
arrangements may comprise the adjustment of the
facing units to a required horizontal and vertical
alignment, batter or slope to compensate for the
anticipated gradual deformation of the reinforced fill
structure itself but not for settlements or movements
of the foundation.
80.5.4 The horizontal spacing with respect to
overlapping, alignment and level, and the vertical
alignment, batter or slope of any new course of
facing units or formwork shall be checked and
adjusted if needed, during the construction.
80.5.5 Particular attention shall be paid to the
horizontal spacing - with respect to overlapping,
alignment and level, as well as the vertical
alignment, batter or slope of the initial course, as
accuracy in this phase helps to ensure a rapid and
well aligned construction of the complete structure.
80.5.6 Jointing material and bearing pads, if any are
required by the design, shall be installed, as any new
course of facing units is put in place and secured.
FIG. 138 TYPICAL BRACINGS ARRANGEMENT FOR PANEL ERECTION
FIG. 139 TYPICAL CLAMPS
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FIG. 140 TYPICAL WOODEN WEDGE
80.5.7 A recommended panel placement sequence is illustrated in the Fig. 141 below.
FIG. 141 PANEL PLACEMENT FOR INITIAL COURSE
80.6 Placing Drainage Material
80.6.1 Drainage bay should be provided behind
facing panels having minimum width of 600 mm.
The drainage material shall consist of clean crushed
stone or gravel (without any sharp edges).
80.6.2 Drainage material shall confirm to the
specifications mentioned in the material
specification chapter. One test is recommended per
250 cum of drainage material.
80.6.3 Alternatively, drainage composite shall be
provided behind reinforced soil wall panel all along
the wall length.
80.6.4 If the foundation of the structure is not free
draining, a longitudinal drainage trench, or a porous
or open jointed drainage pipe of suitable size, or a
geo-composite drain shall be placed at the base of
the structure to collect water and bring it to the site
drainage system. The omission of joint filler from
the vertical joints in the embedded depth of panel
facings can normally allow water to pass through the
facing without the need for weep holes.
80.6.5 Where water flow is expected from the
retained soil chimney drain or geo-composite drains
shall be placed.
80.6.6 In cases of water flows a drainage blanket of
sufficient thickness, or a geo-composite shall be
constructed and discharged beyond the toe. If
required this blanket may be continued up along the
face of the temporary excavation.
80.6.7 Any drainage material shall be designed to
avoid loss of reinforced fill or adjacent soil into the
drain to avoid chocking.
80.6.8 Special drainage considerations shall apply to
partially or temporarily submerged reinforced fill
structures.
80.6.9 Drainage considerations for reinforced slopes
shall follow the procedures detailed above. In
addition, it may be necessary to ensure that
precipitation on the face of the slope does not lead to
washout.
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80.7 Spreading Soil Backfill (Reinforced and
Retained Backfill) and Compaction
80.7.1 Placement and compaction of fill shall be
executed with great care as the performance of a
reinforced fill structure is mainly influenced by the
nature of the backfill and the consistent manner in
which it is placed and compacted.
80.7.2 The specification of reinforced (select) fill
and retained fill bath shall be as per specifications
provided in material chapter. One test is
recommended per 1 500 cu.m. of material for both
reinforced fill and retained fill.
80.7.3 Prior to the commencement of construction, a
method for compaction of the fill shall be
established which, if specified, may include field
trials.
80.7.4 Equipment compatible with the proposed
method shall be provided to achieve the compaction
requirements set up by the design.
80.7.5 The grading and the moisture content of the
fill material shall be checked periodically during
construction to assure compliance with the design
specifications, especially whenever the appearance
or behavior of the material changes noticeably.
80.7.6 The deposition, spreading, levelling and
compaction of the fill should be carried out generally
in a direction parallel to the facing or the sloped face.
80.7.7 Care shall be taken to ensure that the
reinforcing elements and the facing, if any, are not
damaged during deposition, spreading, levelling and
compaction of the fill. No machines or vehicles shall
run directly on the reinforcements.
80.7.8 The fill within 1 m of the face may be
compacted using adequate light compaction
equipment. Where small compaction equipment is
used, the thickness of the layers shall be adjusted as
needed to obtain the compaction requirements. All
vehicles, and all construction equipment weighing
more than 1 500 kg shall be kept at least 1 m away
from the facing or the face of slopes without facing.
80.7.9 Fill should be placed and compacted in lifts.
Thickness of lift (not more than 200 mm) should be
consistent with the compaction equipment used and
the degree of compaction to be achieved.
If necessary, sprinkle water to bring the water
content close to the optimum moisture content.
80.7.10 The thickness of the lifts of backfill shall be
within the limits specified by the design and such
that it allows compaction to the required density.
It should be a sub-multiple of or equal to the vertical
spacing of reinforcement.
80.7.11 Specific care shall be taken for the
compaction of the fill near the facing, to avoid any
damages of the facing elements, the connected
reinforcements and to minimize deformations.
Special attention shall be paid to confined spaces,
such as the corners of a structure as mentioned in
79.4.1.
80.7.12 At the end of each day's work the surface of
the compacted fill should be left at a slight
inclination (2 percent to 4 percent) away from the
facing or the sloped face and sealed with a smooth
compactor to ensure that any surface water is guided
away to a suitable outlet. This is critical during
monsoon season as surface runoff towards facing
will result in movement of facing, soil erosion and
contamination of drainage media.
80.7.13 The rear of the structure should be backfilled
by phasing the work in order to ensure the
contemporaneous deposition of the retained fill
material.
80.7.14 The sequence of fill placement over soft or
very soft ground may be specified within the design.
If not, care should be taken to ensure that the
sequence of filling, including any trafficking by
construction plant, at no time exceeds the bearing
capacity of the underlying ground.
80.8 Laying of Reinforcement, Connection
between Facing and Reinforcement
80.8.1 The reinforcement shall be laid on an even
surface and connected to the facing, if applicable,
using the connection method particular to the facing
system as specified by the design.
80.8.2 It shall be ensured that the flexible
reinforcement is taut and that any slack has been
removed, in order to minimize any deformation
during the mobilization of tensile forces in the
reinforcement. This may be achieved by pulling the
reinforcement tight and holding in this position
while it is covered with fill.
80.8.3 Reinforcement should be placed as
perpendicular as possible to the facing or to the
sloped face unless specified otherwise in the design.
A transverse overlap may be used at the junction of
adjacent pieces of sheet type reinforcement if
specified in the design.
80.8.4 In the presence of obstacles such as pipes,
columns, piles, manholes etc, it may be necessary
to skew or shift a reinforcement from its designated
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location in either the horizontal or vertical direction.
For sheet-type reinforcements it may be necessary to
cut a hole into the reinforcement. Unless such
alterations are explicitly permitted by the design
they shall be ratified by the designer.
80.8.5 Reinforcement with vertical bends should be
placed on a preformed mound of backfill. Sharp
bends which affect the reinforcement strength shall
be avoided unless allowed for in the design.
80.8.6 Reinforcements should extend in one
continuous piece in the main load carrying direction.
Where joints in that direction are unavoidable, the
design shall specify an appropriate on-site jointing
method. The joints may be formed using methods
such as bolting, welding, bodkin joints, etc or
designed overlaps, respective to the type of
reinforcement and as per the detailing provided by
the designer. Such joints should be provided away
from the most critical slip surface in the stable mass
of the soil.
80.8.7 For Block facing walls with an outside
90° corner, it is important that grid layers do not
overlap at the corner. Place the first grid layer per
plan at its design elevation and length. On the corner
and on the next course of blocks, place a layer of grid
perpendicular to the previous layer of grid and these
steps should be repeated for successive specified
grid layers.
80.8.8 For Inside 90° corner, extend the grid past one
edge of the wall by a minimum of 600 mm. Along
the other edge, place the grid to the corner. At the
next designed grid layer, alternate the edge on which
the grid is extended past the corner and repeat the
steps for successive specified grid layers.
80.8.9 Polymeric reinforcement may be prone to
degradation when exposed to sunlight and therefore
should be covered with fill within a specified time
of laying. Where no such time is specified, exposed
reinforcement should be covered within 24 h of
placement.
80.8.10 In general, the placement of sheet material
may be disrupted by wind uplift. Where this is likely,
the material should be locally ballasted.
80.9 Successive Face Element Erection and
Batter
80.9.1 Clean the top surface of the facing unit placed
in the first row with a stiff broom or brush to remove
all soil, debris etc before proceeding with
subsequent layer.
80.9.2 Check the reduction in batter due to outward
movement of panels during placement and
compaction of fill to achieve the final batter if
applicable, as per the system. If the batter has not
reduced, maintained required batter by rework and
proceed for next course of placement. Initial batter
for panel shall be decided as per the type of the fill
material, final batter for the wall shall be as per the
design and drawings.
80.9.3 Bearing pads shall be placed on the top of
previously placed panel facing units and then next
layer of facing elements shall be placed over them.
Set them to the required batter using wooden
wedges. Check levels and alignment of the panels.
80.9.4 Fix the nonwoven geotextile filter strips
behind vertical and horizontal joints.
80.9.5 Block facing units do not require bearing pad
units in between layers. However, all other
installation parameters pertaining to alignments, line
and levels remain same.
80.10 Wrap Around Construction
Manufacturer and designer method statement shall
be followed for the construction sequences for wrap
around wall.
80.11 Top of the Wall Element Erection
At the top of the upper most facing units, provide a
cast in-situ coping beam to achieve the required
longitudinal profile as per the drawings.
80.12 Construction and Serviceability Tolerances
The construction tolerances shall be as mentioned
in Table 39.
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Table 39 Tolerances for Construction
(Clause 80.12)
Sl No. Characteristics Tolerance
(1) (2) (3)
i) For precast RCC panels:
a) All dimensions within ± 5 mm
b) Evenness of front face ± 5 mm over 1 500 mm
c) Differences between length of two diagonals, Max
d) Thickness
5 mm
+ 5 mm
ii) For modular blocks:
a) Dimension for length and width ± 2.5 mm
b) Dimension for height ± 1.5 mm
iii) For faces of retaining walls and abutments:
a) Location of plane of structure ± 50 mm – metallic reinforcement
± 75 mm – synthetic reinforcement
b) Bulging (vertical) and bowing (horizontal) ± 20 mm in 4.5 m template (metallic)
± 30 mm in 4.5 m template (synthetic)
c) Steps at joints ± 10 mm
When vegetation is to be used the face shall provide
a suitable medium for the establishment and
continued growth of the vegetation. For a vegetated
face several interrelated aspects need to be
considered, including, the climate, site location,
aspect, altitude, amount and frequency of
precipitation, exposure, form of facing, erosion
resistance capability.
NOTE — Acceptance criteria for any out of tolerance wall
facing should be established on the basis of serviceability
criteria at the start of the work. C and O, remediation or
retrofitting for such deviations is not in the purview of this
document
80.13 Supervision, Testing, Monitoring and
Record Keeping
80.13.1 Supervision
A suitably qualified and experienced person shall be
responsible for checking that the construction
complies with the design, appropriate/approved
construction methodology and all other contract
documents.
80.13.2 Monitoring
Monitoring of all works connected with the
execution of various stages of reinforced fill
construction shall be in accordance with the method
statement made to fulfil the design and the project
specification. Proper instrumentation shall be
adopted for critical structures.
80.13.3 Testing
The testing for reinforced fill structures shall be in
accordance with applicable standard or the
specifications of the design. The records of any
testing shall provide the test method and procedure,
test results and the conclusions and relevance to the
reinforced fill structure.
80.13.4 The level of supervision, monitoring and
testing shall be in accordance with the specification
of the design, (see 37).
80.13.5 The type, extent and accuracy of monitoring
and testing requirements on and off site should be
clearly shown in the specification and organized
before work commences on site.
80.13.6 Unless specified in the design, supervision
should relate to:
a) Site preparation — Topography,
geotechnical data, set-up, geometry of
excavations, foundation pad (if applicable);
b) Fills — Conformity with design:
characteristics, placing and compaction,
monitoring and testing when necessary;
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c) Reinforcement — Conformity with design,
reception, handling, storage, placing,
damage during installation, prestressing of
reinforcement (if applicable), monitoring
and testing when necessary;
d) Facing materials — Conformity with
design, installation of facing elements,
alignments and displacements, finishings,
monitoring and testing when necessary; and
e) Drainage — Base/foundation, back slope,
layer drainage during installation, other
drainage systems needed.
80.14 Records During Construction
If required, records shall be made of relevant aspects
of the construction including: weather conditions,
progress of the works, supervision, tests and
observations etc.
80.15 Records at the Completion of the Works
If required records shall be made of the as-built
works including:
a) Information showing the ‘as-built’
reinforced fill works in full detail
especially any changes from the initial
drawings and specifications;
b) Details of materials used;
c) The position of all culverts, fences,
underground cables, pipes and the like;
d) Details of the foundation soils and
conditions and other relevant geotechnical
conditions;
e) Any restrictions concerning surcharge
loads which the construction may support;
f) Any special features or precautions that
may be necessary if the structure has to be
demolished;
g) Details and location of any durability
samples installed together with
recommendations for the method and times
for their extraction and subsequent testing;
and
h) Any particular recommendations for
inspection and maintenance.
Records should be kept after the end of the works for
the time period stated in the project specification.
80.16 Instrumentation
a) During the execution of reinforced soil
walls, the longitudinal and vertical
alignment of RS wall facing shall be
maintained. It is advisable to
measure/record the desired RS wall batter
with the help of surveying instruments such
as total station;
b) It is advisable that the RS wall panels shall
be monitored and recorded timely for any
further panel movements post RS wall
construction in order to avoid failure at
later stage; and
c) For RS wall at locations where weak
foundation soil is present and post
construction settlement is accepted after
performing suitable ground improvement
schemes. The post construction settlements
shall be measured with proper instruments.
81 RELEVANT POINTS TO BE
INCORPORATED IN CONSTRUCTION
DRAWINGS
Following points shall be incorporated in the
construction drawings:
a) RS wall key plan, typical cross sections,
elevation drawings, etc shall be properly
shown with all the required details which
are required at site for construction;
b) Details such as RS wall curvature, curve
length, structure skew details, acute corner
details, traffic movement direction, cross
drainage works, etc shall be shown in the
general arrangement drawings;
c) Length and grade of soil reinforcement,
spacing, panel type, foundation bearing
pressure (required SBC), distance of RS
wall from abutment foundation, sloping
surcharge height, etc shall be shown in the
elevation drawings;
d) The ground improvement scheme shall also
be shown in the typical cross section and
extent of GI carried out shall be shown in
(as built) elevation drawings;
e) The slip joint details in closing wall and
longitudinal wall wherever it is required
shall be shown in the drawings;
f) Service road level or existing ground levels
shall be mentioned in the elevation
drawings;
g) The drain invert levels shall be shown for
the cross drainage works; and
h) The plan view showing a gap (20 mm to
40 mm) between the friction slab and the
approach slab interface shall also be shown
in the construction drawings as shown in
Fig. 142. The gap shall be filled with
compressible filler material and covered
with bituminous coating in order to avoid
any ingress of water penetration.
Any other additional points shall also be included
with appropriate notes covering various
construction aspects of RS wall.
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82 SALIENT POINTS
Do’s and Don’ts
a) Adequate geotechnical investigations for
foundation shall be carried out;
b) Typically, erroneous or inadequate data for
classification, shear strength, consolidation
parameters etc may cause excessive
differential/total settlement resulting in
bulging/leaning of panels and uneven
riding surface in plan or bearing capacity
failure leading to excessive distortion or
collapse;
c) Soil investigations regarding borrow area
material to be used as reinforced and
retained soil. If the fill material contains
high percentage of fines, it may
compromise with the frictional transfer and
cause difficulty in compaction, build-up of
hydrostatic pressure and there by internal
fill movements resulting in bulging and/or
leaning of facing elements. The
specifications of reinforced and retained
fill provided in Section 3 shall be followed;
d) Facing moulds dimensions shall be within
the allowable tolerance limit before starting
the casting of facing elements;
e) Ensure that the bed is levelled, no loose
pockets/slush are present prior to placing of
concrete for levelling pad;
f) Mark the layout of outer face of bottom
panel on levelling pad before erection;
g) Check the alignment of the wall (horizontal
and vertical) after completion of each layer
of compacted fill material;
h) Ensure there are no pits/depressions in
drainage bay/fill material before laying of
reinforcement;
j) Ensure no slack/wrinkles develop in the
tensioned reinforcement before and during
grading of fill material;
k) Ensure no vehicle is allowed to move
directly over the reinforcement, a minimum
cover of 150 mm of fill material should be
placed over reinforcement before any
vehicle/equipment is allowed;
m) Do not allow any movement of heavy
vehicle/heavy roller/equipment within
1 500 mm from the wall facing;
n) Do not allow any change (in fill material,
reinforcement type and orientation,
connection arrangement etc) during
construction without the prior approval of
the design engineer, once the system is
accepted by the approving authority;
p) Do carry out execution of service road prior
to reinforced soil wall execution. In no case
reinforced soil wall foundation left open to
ensure adequate embedment all the time;
FIG. 142 TYPICAL PLAN VIEW FOR APPROACH SLAB AND FRICTION SLAB INTERFACE
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q) At acute angle corners of structures in skew
and in any excavated area (near abutment,
cross drainage works etc), to avoid
differential settlement, fill with self-
compacting material (aggregates/gravels)
with sluicing of sand;
r) Do not allow direct transfer of the load over
the facing element, through crash barrier,
approach slab, gap slab etc. A gap shall be
maintained between the facing element and
crash barrier which shall be properly filled
with compressible fill; and
s) Proper camber/super elevation shall be
maintained for effective drainage.
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ANNEX A
(Clause2)
LIST OF REFERRED STANDARDS
IS No./Other Standard Title
IS 456 : 2000 Plain and reinforced
concrete — Code of
practice (fourth revision)
IS 432 (Part 2) : 1982 Mild steel and medium
tensile steel bars and
hard-drawn steel wire for
concrete reinforcement:
Part 2 Hard-drawn steel
wire (third revision)
IS 1364 (Part 3) : 2018/
ISO 4032 : 2012
Hexagon head bolts, screws
and nuts of product
Grades A and B: Part 3
Hexagon nuts, style 1 (size
range M 1.6 to M 64)
(fifth revision)
IS 1367 (Part 13) :
2020/ISO 10684 :
2004
Hot dip galvanized coatings
on threaded fasteners
(third revision )
IS 3400 Methods of test for
vulcanized rubbers:
(Part 1) : 2021/
ISO 37 : 2017
Tensile stress-strain
properties (fourth revision)
(Part 4) : 2012/
ISO 188 : 2011
Accelerated ageing and
heat resistance (third
revision)
(Part 6) : 2018/
ISO 1817 : 2015
Determination of the effect
of liquids (fourth revision)
(Part 10) Compression set,
(Sec 1) : 2022/
ISO 815-1 : 2019
At ambient or elevated
temperatures (third
revision)
(Sec 2) : 2022/
ISO 815-2 : 2019
At low temperatures
(third revision)
(Part 20) : 2018/
ISO 1431-1 : 2012
Resistance to ozone
cracking — Static strain
test (second revision)
IS 4759 : 1996 Hot-dip zinc coatings on
structural steel and other
allied products —
Specification (third
revision)
IS 4968 (Part 3) : 1976 Method for subsurface
sounding for soils: Part 3
Static cone penetration test
(third revision)
IS 5529 (Part 1) : 2013 In-situ permeability test:
Part 1 Test in overburden
— Code of practice
(second revision)
IS 7887 : 1992 Mild steel wire rod for
general engineering
purposes — Specification
(first revision)
IS 11309 : 2023 Method for conducting
pull-out test on anchor
bars and rock bolts
(first revision)
IS 11720 (Part 5) :
1993
Methods of test for
synthetic rubber: Part 5
Determination of ash
IS 13094 : 2021 Selection of ground
improvement techniques
for foundation in weak
soils — Guidelines (first
revision)
IS 13162 Geotextiles — Methods of
test:
(Part 2) : 1991 Determination of resistance
to exposure of ultraviolet
light and water (xenon-arc
type apparatus)
(Part 3) : 2021/
ISO 9863-1 : 2016
Determination of thickness
at specified pressures:
Part 3 Single layers
(first revision)
(Part 4) : 1992 Determination of puncture
resistance by falling cone
method
IS 13365 (Part 1) :
1998
Quantitative classification
system of rock mass —
Guidelines: Part 1 Rock
mass rating (RMR) for
predicting of engineering
properties
IS 14293 : 1995 Geotextiles — Method of
test for trapezoid tearing
strength
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IS 14294 : 1995 Geotextiles — Method for
determination of apparent
opening size by dry sieving
technique
IS 14324 : 1995 Geotextiles — Methods of
test for determination of
water permeability —
Permittivity
IS 14716 : 2021 Geosynthetics — Test
method for the
determination of mass per
unit area of geotextiles and
geotextile-related products
(first revision)
IS 15328 : 2003 Unplasticized non-pressure
polyvinyl chloride
(PVC-U) pipes for use in
underground drainage and
sewerage systems —
Specification
IS 15736 : 2007 Geological exploration by
geophysical method
(electrical resistivity) —
Code of practice
IS 16014 : 2018 Mechanically woven,
double-twisted, hexagonal
wire mesh gabions, revet
mattresses, rock fall
netting and other products
for civil engineering
purposes (galvanized steel
wire or galvanized steel
wire with polymer coating)
— Specification (first
revision)
IS 16237 : 2014 Geo-synthetics — Method
for determination of
apparent opening size by
wet sieving
IS 16342 : 2015 Geosynthetics — Method
of test for grab breaking
load and elongation of
geotextiles
IS 16352 : 2020 Geosynthetics — High
density polyethylene
(HDPE) geomembranes for
lining — Specification
(first revision)
IS 16362 : 2020 Geosynthetics —
Geotextiles used in
subgrade stabilization in
pavement structures —
Specification (first
revision)
of test for measuring
pullout resistance of
geosynthetics in soil
(first revision)
of test for biological
clogging of geotextile or
soil/geotextile filters
IS 16732 : 2019 Galvanized structural steel
— Specification
IS 17363 : 2020 Geotextiles and geotextile-
related products —
Screening test method for
determining the resistance
to liquids
IS 17365 : 2020/
ISO TR 20432 : 2007
Guidelines for the
determination of the long-
term strength of
geosynthetics for soil
reinforcement
Determination of damage to
geosynthetic caused during
installation
Polymeric strip/geostrip
used as soil reinforcement
in retaining structures —
Specification
IS 17373 : 2020 Geosynthetics — Geogrids
used in reinforced soil
retaining structures —
Specification
IS 17483 Geosynthetics — Geocells
— Specification:
(Part 1) : 2020 Load bearing application
(Part 2) : 2020 Slope erosion protection
application
ISO 4097 : 2020 Rubber, ethylene-
propylene-diene (EPDM)
— Evaluation procedure
193
To access Indian Standards click on the link below:
https://www.services.bis.gov.in/php/BIS_2.0/bisconnect/knowyourstandards/Indian_standards/isdetails/
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ANNEX B
(Clause3)
TERMINOLOGY
For the purpose of this standard, the following
definition shall apply;
B-1 REINFORCED SOIL
This is a general term which refers to the use of
placed or in situ soil or other material in which
tensile reinforcements act through interface friction,
bearing or other means to improve stability.
B-2 REINFORCED SOIL WALL
This is a form of reinforced soil that incorporate
planar reinforcing elements in constructed
earth-sloped structures with face inclinations of
more than 70 degrees.
B-3 REINFORCED SOIL SLOPE
This is a form of reinforced soil that incorporate
planar reinforcing elements in constructed
earth-sloped structures with face inclinations of less
than 70 degrees.
B-4 REINFORCED SOIL FOUNDATION
This is general term which refers to the use of placed
or in situ soil or other material in which tensile
reinforcements act through interface friction,
bearing or other means to improve stability
B-5 REINFORCED SOIL TRUE ABUTMENT
This is reinforced soil in which in addition to
retaining earth, the reinforced fill supports a bridge
or viaduct which transmits relatively large vertical
and horizontal forces to the reinforced fill through a
footing which is directly placed on the reinforced
fill.
B-6 SHORED REINFORCED SOIL WALL/
SLOPE
This is a reinforced soil mass constructed in front of
the shored wall or slope.
B-7 BASAL REINFORCED EMBANKMENTS
These are earthen embankments constructed on poor
ground in which the stability of the embankment is
enhanced by placing one or more layers of
reinforcements or a mattress across the full width of
the embankment at its base.
B-8 METALLIC STRIPS
These are one type of reinforcement in the form of
strips used in reinforced soil.
B-9 GEOSYNTHETICS
The generic classification of all synthetic materials
used in geotechnical engineering applications.
B-10 GEOGRIDS
These are deformed or nondeformed netlike
polymeric material used with foundation, soil, rock,
earth, or any other geotechnical engineering-related
material as an integral part of the human-made
project structure or system.
B-11 GEOTEXTILES
These are permeable textile (natural or synthetic)
used with foundation, soil, rock, earth, or any other
geotechnical engineering-related material as an
integral part of a human-made project, structure, or
system.
B-12 GEOSTRIP
This is a polymeric strip used in civil engineering
application usually made up of high tenacity, high
modulus polyester tendons encased within
polyethylene sheathing.
B-13 CAPACITY DEMAND RATIO (CDR)
The ratio of the factored resistance to the factored
load is defined as the capacity demand ratio (CDR).
B-14 INEXTENSIBLE REINFORCEMENTS
strains less than or equal to 1 percent.
B-15 EXTENSIBLE REINFORCEMENTS
strains greater than 1 percent.
B-16 ANCHORED EARTH STRUCTURES
This is a structural element installed through the
rock or soil to transfer the tensile forces developed
in the structure to the ground.
IS 18591 : 2024
194
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B-17 MULTI-TIERED WALLS
A tiered retaining wall system is a series of two or
more stacked walls, each higher wall set back from
the underlying wall.
B-18 BACK-TO-BACK WALLS
These are reinforced soil walls can be used to solve
problems in locations of restricted right-of-way
(ROW) and at marginal sites with difficult
subsurface conditions and other environmental
constraints.
B-19 GEO-COMPOSITE
It is one of the geosynthetics made from a
combination of two or more geosynthetic types.
B-20 POLYMERIC REINFORCEMENT
This is a generic term that encompasses geosynthetic
materials used in geotechnical engineering.
B-21 TRAPEZOIDAL RS WALLS
Trapezoidal RS walls are basically comprised of
some type of reinforcing element in the soil fill to
help resist lateral earth pressures with trapezoidal
section. Walls with a trapezoidal cross section
should only be considered where foundations are
formed by excavation into rock or when good
foundations exist.
B-22 SOIL REINFORCEMENT
This is a tensile reinforcing element (inclusions) in
the soil placed to improve the strength of the soil
significantly such that the vertical face of the soil
reinforcement system is essentially self-supporting.
B-23 Reinforced fill- This is the fill material in
which the reinforcements are placed.
B-24 RETAINED BACKFILL
Fill material located behind the reinforced soil mass.
B-25 FACING SYSTEM
This is a system may be ‘rigid’, ‘semi-rigid’ or
‘flexible’ and are selected to retain the fill material
to prevent local slumping and erosion of steeply
sloping faces, and to suit environmental
requirements.
B-26 LEVELLING PAD
This is a pad at foundation level on which facing
units are placed.
B-27 GABIONS
Prepared from pre-assembled rectangular cages
made of double twisted steel woven wire mesh filled
with rocks/boulders.
B-28 LRFD
This is a design approach based on the principle that
the strength of various materials is scaled down by
some factors while the applied loads are scaled up
by some factors, and thereby the structural elements
are designed using reduced strength and increased
loads.
B-29 COVERAGE RATIO
This is a defined as the ratio of effective width of
reinforcement to the centre-to-centre horizontal
spacing between the reinforcements.
B-30 GEOSYNTHETIC REINFORCEMENT
Generic term that encompasses geosynthetic
materials used in geotechnical engineering such as
geotextiles, geogrids and geostrips
B-31 STEEP SLOPES
Reinforced soil slopes with face inclinations steeper
than 45° to the horizontal.
B-32 SHALLOW SLOPES
Reinforced soil slopes with face inclinations less
than or equal to 45° to the horizontal.
B-33 GEONETS
This is a geosynthetic consisting of parallel sets of
ribs overlying and integrally connected with similar
sets at various angles.
B-34 GEOCELLS
Geocells are three-dimensional, permeable,
polymeric (synthetic or natural) honeycomb, or
similar cellular structure, made of linked strips of
geosynthetics.
195
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B-35 ROLLED EROSION CONTROL
PRODUCTS
These are three-dimensional geosynthetics erosion
control mats.
B-36 MIXED OR FALSE ABUTMENT
This is a abutment in which bridge beams are rested
on a RCC cap supported by a group of piles which
are embedded inside reinforced soil mass.
B-37 BASAL REINFORCEMENT
This is a reinforcing element placed at the base of
embankments to provide additional resistance to
foundation failure, control of settlements, transfer of
load onto rigid inclusions, or spanning over voided
zones.
ANNEX C
(Clause4)
SYMBOLS
IS 18591 : 2024
196
a = scale correction factor
α = scale correction factor (generally
1.0 for metallic reinforcement
and 0.8 for geosynthetics
reinforcements)
A = maximum ground acceleration
coefficient
Ac = design cross section area of the steel
Am = design acceleration coefficient
Ah = horizontal seismic coefficient
Av = vertical seismic coefficient
σv = factored vertical pressure
σH = horizontal stress
B = effective width of soil reinforcement
b = gross width of the strip, sheet or grid
bf = width of applied load. for footings
which are eccentrically loaded (for
example, bridge abutment footings),
set bf equal to the equivalent footing
width b’
by reducing it by 2e, where
e’
is the eccentricity of the footing
load (that is., bf-2e’
).
Bs = horizontal projected width of the
slope face
 = inclination of slope face with
horizontal
reinforcement (number of surfaces)
𝐶𝑐 = compression index
Cf = setback distance-bridge superstructure
𝐶𝑙𝑠 = chloride content within soil sample
from 2 : 1 water : soil extract
𝐶𝑅 = core recovery
CT
cu
cut
= impact load on barriers
= undrained shear strength
= nominal total stress cohesion of the
foundation soil
𝐶𝑙𝑤 = chloride content within water sample
H = factored horizontal stress due to
pressure generated from external
surcharges if any
CDR
d
f
= capacity demand ratio
= embedment depth
= angle of friction between retained
backfill and reinforced soil
dh
ds
Ds
= minimum depth for horizontal slope
= minimum depth for sloping toe
= thickness of soft foundation strata
below reinforced soil slope
D1 = effective width of applied load at any
depth, calculation shown above
𝐷𝐵 = disturbed bulk soil sample
𝐷𝑃 = disturbed soil sample from spt soil
sampler
𝐷𝑆 = disturbed soil sample from cutting
edge of undisturbed soil sampler
𝐷𝐶𝐷 = consolidated drained direct shear test
𝐷𝐶𝑈 = consolidated undrained direct shear
test
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𝐷𝑈𝑈 = unconsolidated undrained direct
shear test
𝐷𝐶𝐷𝑃 = consolidated undrained direct shear
test
e
𝑒0
= eccentricity
= initial or field void ratio
eB
EH
= eccentricity for bearing calculation
= earth pressure on reinforced soil
zone due to retained soil mass
EQ
ES
= earthquake load (seismic load)
= crash barrier-friction slab load or
w-beam load as a strip footing, etc
EV = vertical pressure or weight of
reinforced soil zone, sloping
surcharge weight, dead load due to
pavement layers, etc.
F
(F)
= factor of safety
= frictional and cohesive forces acting
along the potential failure plane
F1
F2
= lateral force due to earth pressure
= lateral force due to traffic surcharge
F*
fr
= pullout resistance factor
= effective friction angle of reinforced
soil
fb = effective friction angle of retained
backfill
fy
(FL)
FS
fcu
= yield stress of steel
= horizontal shear
= target safety factor
= characteristic compressive strength
of concrete
fyd
fcud
= design yield strength of steel
= design compressive strength of
concrete
FLL
FDL
𝐺𝑆
= horizontal inertia of bridge ll
= horizontal inertia of bridge dl
= specific gravity
gb
gf
gr
= unit weight of retained backfill
= partial safety factor for loads
= unit weight of reinforced soil
gfd = unit weight of foundation soil
ΩmD = soil resistivity, where suffix d shall
indicate the compass bearing of the
direction of measurement
H = design height of reinforced soil wall
H = height of reinforced soil slope
heq = equivalent uniform soil surcharge
height
HLcreep = horizontal reaction for creep and
shrinkage forces that occur
HLtemp = horizontal reaction for temperature
effects that occur
HLLmax = maximum horizontal live load
reaction (hllmax) for
braking/traction forces
LH = increment of horizontal stress due to
the horizontal loads at the base of the
wall or layer due to overburden
pressure
𝑘𝑙 = laboratory permeability
𝑘𝑓 = field permeability
kb = vertical seismic coefficient
kh = horizontal seismic coefficient
Kr = coefficient of horizontal earth
pressure in the reinforced soil zone
Kab = horizontal earth pressure coefficient
KAE = combined static and dynamic earth
pressure coefficient
L = reinforcement length
La = length of reinforcement in the active
zone
L’ = effective foundation width
resisting zone. note that the
boundary between the resisting and
active zones may be modified by
concentrated loadings
Le = length of reinforcement embeded in
the resisting zone
Lf
𝐿𝐿
= length of footing
= liquid limit
LS/LL = live load surcharge (traffic
load)/vehicular live load
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IS 18591 : 2024
198
m = minimum of tangent soil friction
angle
𝑚𝑣 = coefficient of volume
compressibility
MD = disturbing moment
MRS = restoring moment due to shear
strength of the soil along the slip
surface
MRR = restoring moment contributed by the
reinforcements which intersects the
failure surface
𝛿 = inclination of horizontal earth
pressure
(N)
N
NP
= normal reaction of the failure plane
= standard penetration test blow count
= number of discrete reinforcements
per unit width
Pi
𝑃𝑆
= internal dynamic force
= swelling pressure
𝑃𝑐 = pre-consolidation pressure
Pv = dead load (qdl) and live load (qll) of
the bridge superstructure
𝑃𝐼 = plasticity index (liquid limit minus
plastic limit)
𝑝𝐻 = ph value of water sample
PAE
PH
= total static and dynamic thrust
= lateral load due to superstructure and
other concentrated lateral force
PIR = horizontal inertial force of reinforced
soil mass
𝑃𝑀𝑇 = pressure meter test
∆PAE = dynamic (pseudo static) force acting
on bridge footing
qn = nominal bearing resistance
qr
Qv
Qv
’
= factored bearing resistance
= load per unit length of strip footing
= load on isolated rectangular footing
or point load
QDL = dl due to bridge superstructure on
each abutment
QDL = dead load of the bridge
superstructure
QLL
qT
quniform
Rc
RF
RFID
RFCR
𝑅𝑄𝐷
= live load of the bridge superstructure
= load due to traffic surcharge
= uniform meyerhof distribution
= coverage ratio
= total reduction factor
= installation damage reduction factor
= creep reduction factor
= rock quality designation
RFD = durability reduction factor
(SL)
Sh
= vertical strip load (sl)
= centre to centre horizontal spacing
between the reinforcements
Sv = vertical spacing of soil
reinforcement
Seq = equivalent uniform height of soil
Sv
𝑆𝑇
= vertical reinforcement spacing
= sensitivity of soil from vane shear
test
𝑆𝐿 = shrinkage limit
𝑆𝑂𝑥𝑤 = SOX content within water sample
𝑆𝑂𝑥𝑠 = SOX content within soil sample from
2 : 1 water : soil extract
T
Tr
Tal
= tensile strength of reinforcement
= factored tensile resistance
= available long-term tensile strength
of the reinforcement
𝑇𝑈𝑈 = unconsolidated undrained triaxial
test
𝑇𝐶𝑈 = consolidated undrained triaxial test
𝑇𝐶𝐷 = consolidated drained triaxial test
TMAX = maximum factored tensile force in
the reinforcement
Tult = ultimate tensile strength of
reinforcement
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199
𝑇𝐶𝐷𝑃 = consolidated undrained triaxial test
with porewater pressure
measurements
 = inclination of planar failure surface
(sliding wedge) to the horizontal
𝑈𝐵 = undisturbed block soil sample
𝑈𝐶 = unconfined compression strength
test
𝑈𝐷𝑆 = undisturbed soil sample from
sampler
V
𝛻
= dl due to beam seat
= ground water level
V4 = self weight of the reinforced soil
mass
V0 = self weight of soil behind the beam
seat
= nominal vertical stress at the
reinforcement level in the resistance
zone, including distributed dead load
surcharges, neglecting traffic loads
VLLmin = minimum vertical live load reaction
(VLLmin) associated with
maximum braking/ traction forces
𝑉𝑆𝑇𝑈 = vane shear test (undisturbed)
𝑉𝑆𝑇𝐷 = vane shear test (disturbed)
V1, V2
and V3
= dead weight of beam seat
𝜎v-
footing
= increment of vertical stress due to
concentrated vertical surcharge pv
assuming a 2v:1h pyramidal
distribution
W = weight of slice
(W)
(Ws)
= self-weight of the fill in the wedge
= Uniformly distributed surcharge
WP
Wa
ws
𝜔𝑛
loads (ws)
= width of panel
= soil weight of the active zone
= uniformly distributed surcharge load
= natural moisture content
𝛾 = field density
yi = perpendicular distance from the
centre of rotation to the
reinforcement
 = unit weight of fill/soil
𝛾𝑑 = field dry density
γp = load factor for permanent loading
P-EV = load factor corresponding to a
vertical pressure from a dead load
earth fill
P-ES = load factor corresponding to the
earth surcharge loading
γEQ = load factor for live load applied
simultaneously with seismic loads
Z = seismic zone factor
z1 = depth where effective width
∅
intersects back of wall face = 2d1-bf
= resistance factor
φ = resistance factor for soil
reinforcement pullout
≥ = greater than or equal to
𝜎v
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ANNEX D
BORE/PIT LOG AND SOIL TEST DATA SUMMARY
PROJECT: TYPE OF BORING/DRILLING/STYLE OF PIT EXCAVATION:
BOREHOLE/PIT No.: BORE DIAMETER (mm)/PIT SIZE(m):
BOREHOLE/PIT COORDINATES (m): CASING DIAMETER (mm):
GROUND LEVEL (m): MAXIMUM DEPTH OF CASING (m):
GROUNDWATER LEVEL (m): PERIOD OF EXECUTION IN DATES:
Depth
(m)
Unique
symbolization
and
Soil
Description
Sample
Type
CR
(%)
RQD
(%)
Mechanical
Analysis
(percentage
passing)
Consistency
Limits
Natural
Moisture
Content
Standard
Penetration
Number
BIS
Soil
Classification
Unit
Weight
Specific
Gravity
Vane
Shear Test
Strength
Parameters
Consolidation Test
Permeability
Tests
Swelling
Pressure
Free
Swell
Chemical
Tests
on
Water
and
Soil
Remarks
Gravel
(%)
Sand
(%)
Fines
(%)
𝐿𝐿%
𝑃𝐼%
𝑆𝐿%
%
kN/m
3
Undisturbed
kPa
Remoulded
kPa
Type
of
Test
kPa
φ°
P
c
kPa
/
e
0
(Void
Ratio)
k
f
m/s
k
l
m/s
P
s
,
kPa
𝐹𝑆,
%
IS 18591 : 2024
200
ω
n
N
ω
n
G
s
Cc
m
v
kPa
-1
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NOTES
1 Soil resistivity shall be noted separately.
2 One column of corrected N value shall also be added
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ANNEX E
(Foreword)
COMMITTEE COMPOSITION
Geosynthetics Sectional Committee, TXD 30
Organization Representative(s)
The South India Textile Research Association Council,
Coimbatore
DR A. N. DESAI (Chairperson)
Ahmedabad Textile Industry’s Research Association,
Ahmedabad
SHRIMATI DEEPALI PLAWAT
SHRI JIGAR DAVE (Alternate)
Best Geotechnique Pvt Ltd, Mumbai SHRI SATISH NAIK
Central Coir Research Institute, Alappuzha DR S. RADHAKRISHNAN
SHRIMATI SUMY SEBASTIAN (Alternate)
Central Road Research Institute, New Delhi DR P. S. PRASAD
DR PANKAJ GUPTA (Alternate)
Central Soil and Materials Research Station, New Delhi DR R. CHITRA
DR MANISH GUPTA (Alternate)
Charankattu Coir Mfg Co (P) Ltd, Shertallay SHRI C. R. DEVRAJ
SHRI C. D. ATHUL RAJ (Alternate)
Department of Jute and Fibre Technology, Kolkata DR SWAPAN GHOSH
PROF (DR) A. K. SAMANTHA (Alternate)
DKTE Centre of Excellence in Nonwovens, Ichalkaranji SHRI ANIKET S. BHUTE
Ganga Flood Control Commission, Patna SHRI M. K. SRINIVAS
SHRI AMITABH PRABHAKAR (Alternate)
Garware Technical Fibers Ltd, Pune SHRI TIRUMAL KULKARNI
SHRI RAJENDRA GHADGE (Alternate)
SHRI RAVIKANT SHARMA
Geosynthetics Testing Services Pvt Ltd, Ahmedabad
ICAR - National Institute of Natural Fibre Engineering
Technology, Kolkata
DR SANJOY DEBNATH
DR KARTICK SAMANTA (Alternate)
Indian Geotechnical Society, New Delhi DR BAPPADITYA MANNA
DR DEBAYAN BHATTACHARYA (Alternate)
PROF AMIT PRASHANT
PROF A. K. GHOSH
PROF K. RAJAGOPAL
Indian Institute of Technology, Delhi
Indian Institute of Technology, Gandhinagar
Indian Institute of Technology, Madras
Indian Jute Industries' Research Association, Kolkata DR MAHUYA GHOSH
SHRI PALASH PAUL (Alternate)
Indian Jute Mills Association, Kolkatta SHRI S. K. CHANDRA
SHRI J. K. BEHERA (Alternate)
Indian Technical Textile Association, Mumbai DR ANUP RAKSHIT
SHRIMATI RUCHITA GUPTA (Alternate)
International Geosynthetics Society, India Chapter,
New Delhi
SHRI M. VENKATARAMN
DR G. P. PATEL (Alternate)
IS 18591 : 2024
202
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Kusumgar Corporates, Mumbai SHRI Y. K. KUSUMGAR
DR M. K. TALUKDAR (Alternate)
DR ANIL DIXIT
SHRI HARSH KUMAR CHITTORA (Alternate)
Landmark Material Testing and Research Laboratory Pvt
Ltd, Jaipur
Macaferri Environmental Solutions Pvt Ltd, Navi Mumbai DR RATNAKAR MAHAJAN
SHRIMATI MINIMOL KORULLA (Alternate)
Megaplast India Pvt Ltd, Daman SHRI C. V. RAJESH
SHRI TATWADARSI S. TRIPATHY (Alternate)
Ministry of Road Transport Highways, New Delhi SHRI SANJIV KUMAR
Municipal Corporation of Greater Mumbai, Thane DR VISHAL RAMESH THOMBARE
SHRI MANDAR BHALCHANDRA PINGLE (Alternate)
National Highways Authority of India, Ghaziabad SHRI RAKESH PRAKASH SINGH
SHRI MUDIT GARG (Alternate)
National Jute Board, Kolkata SHRI M. DUTTA
Office of the Jute Commissioner, Kolkata SHRI R. K. ROY
SHRI SOUMYADIPTA DATTA (Alternate)
Office of the Textile Commissioner, Mumbai SHRI SIVAKUMAR S.
SHRI SANJAY CHARAK (Alternate)
Premier Polyfilms Ltd, Ghaziabad SHRI AMITAABH GOENKA
SHRI PRAVEEN KUMAR (Alternate)
Rajadhani Institute of Engineering Technology, DR K. BALAN
Trivandrum
RDSO, Lucknow SHRI SANJAY KUMAR AWASTHI
SHRI SANTOSH KUMAR OJHA (Alternate)
Reliance Industries Ltd, New Delhi SHRI V. RAVIKANTH
SHRI RAJENDREN SUBRAMANIAN (Alternate)
Sahastra Engineers Pvt Ltd, Noida SHRI VANKATA MAYUR
Strata Geosystems (I) Pvt Ltd, Mumbai SHRI NARENDRA DALMIA
SHRI SHAHROKH BAGLI (Alternate)
Techfab India, Mumbai SHRI ANANT KANOI
SHRI SAURABH VYAS (Alternate)
Texel Industries Limited, Gandhinagar SHRI SHAILESH R. MEHTA
SHRI ANIL SHARMA (Alternate)
The Bombay Textile Research Association, Mumbai DR SREEKUMAR
SHRI G. R. MAHAJAN (Alternate)
The Synthetics Art Silk Mills Research Association,
Mumbai
DR MANISHA MATHUR
SHRIMATI ASHWINI SUDAM (Alternate)
In Personal Capacity [37/1 Satyen Park, Thakurpukur,
Kolkata - 700104]
SHRI P. K. CHOUDHURY
In Personal Capacity [104, Kanchanban, A. W. Vartak
Marg, Vile Parle (East), Mumbai - 400057]
SHRI V. N. GORE
203
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In Personal Capacity [Bhakta Nivas, 12-1-170/46
P, Hanuman Nagar, Jaipuri Colony, Nagole,
Hyderabad - 500068]
DR G. V. RAO
In Personal Capacity [A201, Patel Park, Sector 21, Greater
Khanda Link Road, Kamothe - 410209]
SHRI V. K. PATIL
In Personal Capacity [1803, Claremont A, Lodha Luxuria,
Majiwada, Thane - 400601]
SHRI JAYANT NASHIKKAR
BIS Directorate General SHRI J. K. GUPTA, SCIENTIST ‘E’/DIRECTOR AND HEAD
(TEXTILE) [REPRESENTING DIRECTOR GENERAL
(Ex-officio)]
Member Secretary
SHRI HIMANSHU SHUKLA
SCIENTIST ‘B’/ASSISTANT DIRECTOR
(TEXTILE), BIS
Panel for Formulation of Standard on Geosynthetics — Reinforced Soil Structures
Organization
Indian Institute of Technology, Gandhinagar
Representative(s)
PROF G. V. RAO (Convener)
DR JIMMY THOMAS (Alternate I)
PROF M. VENKATARAMAN (Alternate II)
SHRI KOLLI MOHAN KRISHNA (Alternate III)
Best Geotechnique Pvt Ltd, Mumbai SHRI SATISH NAIK
Central Road Research Institute, New Delhi SHRI GURU VITTAL
CTM Technical Textiles, Ahmbedabad SHRI AMIT AGARWAL
Garware Wall Ropes Ltd, Pune SHRI RAJENDRA GHADGE
Indian Institute of Technology, Madras PROF K. RAJAGOPAL
G-CUBE Consulting Engineers LLP, Pune SHRIMATI DOLA ROY CHOWDHURY
Landmark Material Testing and Research Laboratory Pvt
Ltd, Jaipur
DR ANIL DIXIT
Mumbai
DR RATNAKAR MAHAJAN
Reinforced Earth India Pvt Ltd, New Delhi SHRI ATANU ADHIKARI
Strata Geosystems (I) Pvt Ltd, Mumbai SHRI SHAHROKH BAGLI
Techfab India, Mumbai SHRI SAURABH VYAS
In Personal Capacity (A201, Patel Park, Sector 21,
Greater Khanda Link Road, Kamothe - 410209)
SHRI V. K. PATIL
204
In Personal Capacity [Bhakta Nivas, 12-1-170/46
P, Hanuman Nagar, Jaipuri Colony, Nagole,
Hyderabad - 500068]
PROF AMIT PRASHANT
Maccaferri Environmental Solutions Pvt Ltd, Navi
SHRI SURAJ VEDPATHAK (Alternate)
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In the formulation of this standard, assistance has been derived from the following international standards/
guidelines:
a) BS 8006-1 : 2010 + A1 : 2016 Code of practice for strengthened/reinforced soils and other fills, British
Standards Institution;
b) BS EN 14475 : 2006 Execution of special geotechnical works — Reinforced fill;
c) FHWA-CFL/TD-06-001 Shored mechanically stabilized earth (SMSE) wall system design guidelines,
Central Federal Lands Highway Division, Federal Highway Administration, US Department of
Transportation;
d) FHWA-NHI-10-024 Design and construction of mechanically stabilized earth walls and reinforced soil
slopes – Volume I, National Highway Institute, Federal Highway Administration, US Department of
Transportation; and
e) FHWA-NHI-10-025 Design and construction of mechanically stabilized earth walls and reinforced soil
slopes – Volume II, National Highway Institute, Federal Highway Administration, US Department of
Transportation.
The composition of the Committee responsible for the formulation of this standard is given in Annex E.
In reporting the results of a test or analysis made in accordance with this standard, if the final value, observed or
calculated, is to be rounded off, it shall be done in accordance with IS 2 : 2022 ‘Rules for rounding off numerical
values (second revision)’.
(Continued from second cover)
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Bureau of Indian Standards
BIS is a statutory institution established under the Bureau of Indian Standards Act, 2016 to promote harmonious
development of the activities of standardization, marking and quality certification of goods and attending to
connected matters in the country.
Copyright
BIS has the copyright of all its publications. No part of these publications may be reproduced in any form without
the prior permission in writing of BIS. This does not preclude the free use, in the course of implementing the
standard, of necessary details, such as symbols and sizes, type or grade designations. Enquiries relating to
copyright be addressed to the Head (Publication Sales), BIS.
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewed
periodically; a standard along with amendments is reaffirmed when such review indicates that no changes are
needed; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standards
should ascertain that they are in possession of the latest amendments or edition by referring to the website-
www.bis.gov.in or www.standardsbis.in.
This Indian Standard has been developed from Doc No.: TXD 30 (20465).
Amendments Issued Since Publication
Amend No. Date of Issue TextAffected
BUREAU OF INDIAN STANDARDS
Headquarters:
Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002
Telephones: 2323 0131, 2323 3375, 2323 9402 Website: www.bis.gov.in
Regional Offices: Telephones
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Published by BIS, New Delhi
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IS18591-2024 Geosynthetic Reinforced Soil Structures — Code of Practice

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IS18591-2024 Geosynthetic Reinforced Soil Structures — Code of Practice