Comparative Review on Reinforced Soil and Reinforced Soil Structures

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A comparative review on Reinforced Soil and Reinforced Soil
Structures
Kanika Mehta1, Puneet Hiranandani2, Bhawani Singh Bhati3, Dr. D.G.M. Purohit4
2Junior Engineer-Civil, North Western Railway, Jodhpur, Rajasthan, India
2Lecturer, Department of Civil Engineering, Govt. Polytechnic College, Jodhpur, Rajasthan, India
3Junior Engineer, Urban Improvement Trust, Barmer, Rajasthan, India
4Professor, Dept. of Civil Engineering, M.B.M. Engineering College, J.N.V. University, Jodhpur, Rajasthan, India
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Abstract - Building in layers of compacted soil and
reinforcing material is an old construction method – portions
of the Great Wall of China were built that way and some
sections still remain today. What, is new is the reinforcing
materials that are layered with the soil. Today a combination
of geo-synthetics and a welded steel wire mesh form is finding
success. Construction of building and other civil engineering
structures on weak or soft soil is highly risky because such soil
is susceptible to differential settlements, poor shear strength,
and high compressibility. Varioussoil improvementtechniques
have been used to enhance the engineering properties of soil.
Soil reinforcement is most popular ground improvement
technique. Major advantages of soilreinforcementmethod are
ease of construction, overall economy, time saving etc. Use of
geosynthetics material in place of metal is in practice now.
Form of metal reinforcement were strips, bars etc. But planar
form is the traditional way of reinforcement prepared by
geosynthetics.
Key Words: Reinforced soil, Reinforced soil structure,
Reinforcing Materials.
1. INTRODUCTION
Reinforced soil is a composite material formed by the
association of frictional soil and tension-resistant elements
in the form of sheets, strips, nets or mats of metal, synthetic
fabrics, or fiber reinforced plastics and arranged in the soil
mass in such a way as to reduce or suppress the tensile
strain that might developundergravityandboundaryforces.
By means of friction, the soil transfers to the reinforcement
the forces built up in the earth mass. The reinforcementthus
develops tension and the earth behaves as though, in those
directions in which reinforcement has been placed, it has a
cohesion, the value of which is directly proportional to the
tension in the layers of reinforcement.
All civil engineering structures are constructed on the soil.
Many times engineers encounters with poor or problematic
soil like soft soil, swelling soil etc. In old times engineers
generally avoid construction on such soil, but now a day due
to limitation of land we avoid such solution. Problematicsoil
can be cause of serious damage of structures. So generally
they are replaced by some strong soil or they are treated for
better engineering properties. The techniques utilized for
enhancement of the properties of those soils are known as
ground improvement techniques. Ground improvementcan
be done by some mechanical method, through soil
reinforcement or by adding some admixtures in the soil.
Suitability of particular methods depends upon the site
condition and economy. Among all these methods soil
reinforcement technique is most popularmethodforground
improvement.
2. LITERATURE REVIEW
Since the beginning of civilization, man has attempted to
use soil with some other materials to enable it for being used
for his necessities. Typical uses include use of branches of
trees etc. to support tracks over marshy land to build
hutments and to support large structures. In villages mud
plaster using rice puska is a popular technique to strengthen
the soil. Reinforced soil was used by Babylonians more than
3000 years ago to build ziggurats with woven mats of reeds.
These have also been used in parts of the Great Wall of China
built about 2000 years ago. The Dutch and Romans used
willow to reinforce dives and animal hides.
The recent discovery of methods of preparing high-
modulus polymer materials by tensile drawing, in a sense
“cold working” has raised the possibility of using such
materials as reinforcement in number of civil engineering
applications. Today the major function of such geogrids is in
the area of the reinforcement. The key features of the
geogrids is that the opening between longitudinal and
transverse ribs , called the “apertures” , are large enough to
allow the soil strike through from one side of the geogrid to
the other. The ribs of the geogrids are quite stiff compared to
the fibers of the geotextiles. Also not only rib strength is
important but junction strengthisalsoimportant.Thereason
for this is that the soil strike-through within the apertures
bears against the transverse ribs, which transmit their loads
to the longitudinal ribs via the junctions. The junction is the
location where the longitudinal and transverse ribs are
connected.
The original geogrids were first made in the United
Kingdom by Netlon, Ltd. and were brought in 1982 to the
U.S.by the way of Canada by the Tensar Corp. A similar
product by Tenax Corporation is also available.

Textile material was perhaps first used in road
construction in South Carolina in the early 1930’s. The first
use of a woven synthetic fabric for erosion control was in
1950’s in Florida by Barett. In 1960’s geotextile were
extensively used for erosion control bothinEuropeaswellas
U.S.A. later in 1969, Giroud used non-woven fabricsasafilter
in the upstream face of an earthen dam. In 1971 Wager
initiated use of woven fabrics as reinforcement for
embankments constructed on very soft foundations.
The term “Reinforced Earth” was used after a French
engineer Henry Vidal, who invented this technique. Once
while walking across a dry sandy beach, he noticed that
mounds of drysandcould be made to standatasteeperangle
after the addition of horizontal layers of pine needles. In
modem days, the success of the geotextile depends on
synthetic fibres, which are resistant to degradation by the
micro-organisms present in the soil. Although even today
somefabrics made from natural fibers suchasjute,coiretc.is
also being used.
3. DIFFERENT TYPESOF REINFORCINGMATERIALS
A wide range of alternatives exists in making a choice of
reinforcing materials. However for the selection of
reinforcement the load on the structure and the function of
the structureshould be considered. Moreoverthecostaspect
also should be kept in mind while selecting the type of
reinforcement. Various types of reinforcing materials are
described below.
1. Jute Fibers: The inclusion of Jute fibers constitutes an
effective means of imparting cohesion to remolded and
compacted soil. Due to the inclusion of fiber, impact
resistanceofsoilcanbeconsiderablyimproved.Theinclusion
of jute fibers can be with randomly oriented. Jute fibers
within 2-3 years duration disintegrate with the influence of
water, heat and sun light. Hence, it recommended for
temporary structures.
2. Bamboo Strips: Amongst the various types of
reinforcement usedinreinforcedearthconstruction,bamboo
strips have been in use for long time. They are used both as
strips and mats. But, bamboo deteriorates quickly in wet
conditionsand is also prone to fungus and insectattacks.The
bamboo reinforcements need elaborate preservative
treatment before use. Bamboo, having mechanical and
physical properties incomparisontogeotextileormetals,can
only be used in small or temporary works.
3. Coir: Coir fibers are suitable for various applications
such as, soil stabilization, erosion control, slope protection,
landscaping and reinforcement. Coir fibers rot due to the
ecological natural cycle. Apart from this,coirfibersarehighly
water absorbent. Coir has the greatest tearing strength and
retains this property in wet conditions, which is cost
effective. The coir nets are easy to handle and install. It is a
simple process and does not require skilled labour.
4. Fiber Glass: Fiberglassreinforcementhashighstrength
and isalso corrosion resistant, but it costs more and hence,is
suitable only for special structures and small jobs.
5. Metal Strips: The most commonlyand extensivelyused
reinforcement in earth reinforced structures is mild steel or
high tensile bars and mats. Aluminum strips have also been
tried by some researchers. The steel reinforcement has
excellent physical and mechanical properties.However,steel
reinforcement is subjected to corrosion by chemical or
electrochemical reactions depending upon the physical
properties of the solid, thus necessitating corrosion
protection measures like galvanization, which often renders
it costlier.
6. Geosynthetics: Geosynthetic fibers are made of
Polypropylene, polyethylene, and polyester. They have
become increasingly popular for use as reinforcement in
earth structures in recent years. They are known to be
durable and have a long life. They have sufficient strength
and the mechanical properties to make them suitable for
reinforcement in structures.
4. REINFORCED SOIL (EARTH) STRUCTURE
4.1 Components of Reinforced Earth Structure
Reinforced earth structure consists of three main
components shown in Figure 1, namely
i) Reinforcing element
ii) Soil back fill
iii) Facing element
Fig -1: Components of reinforced earth structure
4.2 Description of reinforcing element:
A variety of materialscan beusedasreinforcingmaterials
.Those that have been used successfully include steel,
concrete, glass fibre, wood, rubber, aluminum and
thermoplastics. Reinforcement may take the form of strips,
grids, anchors & sheet material, chains planks, rope,
vegetation and combinations of these or other material
forms.

4.2.1 Types of reinforcing materials
Strips: These are flexible linear element normally having
their breadth, (b) greater than their thickness, (t).
Dimensions vary with application and structure, but are
usually within the range t=3-5mm, b=5-100mm. The most
common strips are metals. The form of stainless, galvanized
or coated steel strips being either plain or having several
protrusions such as ribs or gloves to increase the friction
between the reinforcement and the fill. Strips can also be
formed from aluminium, copper, polymers and glass fibre
reinforced plastic (GRP). Reed and bamboo reinforcements
are normally categorized as strips, as are chains.
Planks: Similar to strips except that their form of
construction makes them stiff. Planks can be formed from
timber, reinforced concrete or pre stressed concrete. The
dimensionsofconcreteplanksvary;however,reinforcements
with a thickness, (t) = 100 mm and breadth, b= 200–300 mm
have been used. They have to be handled with care as they
can be susceptible to cracking.
Grids and Geo grids: Reinforcing elements formed from
transverse and longitudinal members, in which the
transverse members run parallel to the face or free edge of
the structure and behave as abutments or anchors as shown
in Figure 3. The main purpose is to retain the transverse
members in position. Since the transverse membersactasan
abutment or anchor they need to be stiff relative to their
length. The longitudinal members may be flexible having a
high modulus of elasticity not susceptible to creep. The pitch
of the longitudinal members, pL is determined by their load-
carrying capacityand the stiffness of the transverse element.
The pitch of the transverse elements, PT depends upon the
internal stability of the structure under consideration. A
surplus of longitudinal and transverse elements is of no
consequence provided the soil or fill can interlock with the
grid. Mono and Bi-Oriented grid as shown in Figure 2.
Fig -2: Mono and Bi-Oriented geogrid
Fig -3: Movement of free face of structure
Grids can be formed from steel in the form of plain or
galvanizedweld-mesh,orfromexpandedmetal.Gridsformed
from polymers are known as ―Geo grids and are normally in
the form of an expanded proprietary plastic product.
Sheet reinforcement: May be formed from metal such as
galvanized steel sheet, fabric (textile) or expanded metal not
meeting the criteria for a grid.
Nailing : Earth may be protected by geo synthetics with
earth nailing.
Anchors: Flexible linear elements having one or more
pronounced protrusions or distortions which act as
abutments or anchors in the fill or soil. They may be formed
from steel, rope, plastic (textile)orcombinationsofmaterials
such as webbing and tyres, steel and tyres, or steel and
concrete as shown in Figure 4.
Fig -4: Different Anchors
Composite reinforcement: Reinforcement can be in the
form of combinations of materialsandmaterialformssuchas
sheets and strips, grid and strips and anchors, depending on
the requirements.
In reinforcement with polymers, polymeric joints are
required. Polymeric reinforcement jointsaresubdividedinto
prefabricated joints and joints made during execution of the
works. A number of different jointing systems are in use.
Joints in geotextiles should normally be sewn where load
transference is needed. For polymeric meshes or grid a
bodkin may be employed. A Bodkin joint is an effective
method of joining some polymeric grid reinforcement as
shown in Figure 5.

Fig -5: Bodkin Joint
Care should be taken to ensure that:
1. Bodkins have sufficient cross-sectional area and
strength to avoid excessive deformation
2. Bodkins are not so large as to distort the parent
material causing stress concentrations
3. Joints are pre-tensioned prior to loading, to reduce
joint displacement as the components locktogether.
4.3 Description of Soil Backfill
The fill material for reinforced earth structures shall be
preferably cohesion less and it should have an angle of on
interface friction between the compacted fill and the
reinforcing element of not less than 30, measured in
accordance with IS 13326 Part (I). The soil should be
predominantly coarse grained; not more than 10 percent of
the particles shall pass 75 micron sieve. The soil should have
properties such that the salts in the soil should not react
chemically or electrically with the reinforcing element in an
adverse manner. A wide variety of fill types can be used with
the grids including crushed rock, gravel, industrial slag,
pulverized fuel ash andclay,butfillparticlesgreaterthan125
mm should be avoided.
4.4 Description of facing element
Facings may be hard or soft and are selected to retain fill
material, prevent local slumping and erosion of steeply
sloping faces, and to suit environmental requirements. The
facing shall comprise of one of following:
• Reinforced concrete slabs
• Plain cement concrete form fill hollow block
(precast)
• Masonry construction, rubble facia
• Other proprietary and patented proven system
Common facing used with structure are shown in
Figure 6
Fig -6: Common facing used with structure
4.5 Hard facings
Facing may consist of concrete, steel sheet, steel grids or
mashes, timber, proprietary materials or combination of
these. They should conform to the appropriate material
standard and should be sized by normal design procedures
using the appropriatestandard.Interlockingconcreteblocks,
grout filled bags or Gabions can provide a substantial facing.
These facing shown in Figure7.
Fig -7: Hard Facing
4.6 Soft facings
Generally, external temporary formwork is erected
to support the face during the construction of steep slopes
(>45°). It can take the form of a light weight system of
scaffold tubes and boards or consist ofsomeformofclimbing
shutter. The grids are turned up the face of the framework
and returned into the embankment directly below the next

reinforcement layer. The two grids are connected using a
high density polyethylene bodkin. The soft facing is shownin
Figure 8.
Fig -8: Scaffold frame,Sand Bags (Soft Facing)
Turf and topsoil can be placed on the fill side of the grid
reinforcement as it is turned up the face of the slopetocreate
a natural and aesthetic appearance. Where the vertical
spacing of the main reinforcement is greater than 500mm,
biaxial grid reinforcement isused as intermediatesecondary
reinforcement to provide local stability at the face of the
slope.
4.7 Fasteners between the facing and reinforcing
elements
Fasteners are used to make a connection between the
reinforcement and the facing and take the form of dowels,
rods, hexagon headed screws and nuts and bolts and may
consist one of the following materials:
• Plain steel
• Coated steel
• Galvanized steel
• Stainless steel
• Polymers
The choice of material used to form the fastener should be
compatible with the design life of the structure.
4.8 Drainage
If the embankment becomeswaterlogged and porewater
pressures increase, the magnitude of the tensile forces
induced into the grid reinforcement also increases. Pore
water pressures can be controlled by providing drainage
layers at the back of the reinforced zone in combination with
an under-drain as shown in Figure 9.
Fig -8: Facing with drainage
5. CONCLUSIONS
It can be concluded from the present review
Reinforced soil is a powerful constructiontechniquethat has
demonstrated its value in a wide range of practical
applications, the five most important of which are described
in this book. The versatility of reinforced soil and of
geotextile materials is far from exhausted and new methods
and materials should be expected in the coming years.
Improved polymer materials can only make reinforced soil
more economically attractive. The experience fromthewide
usage of reinforced soil will improve the knowledge and
confidence in the techniques, and provide more data on the
behaviour of reinforced soil structures. Additional
measurements of long-term properties for polymer
reinforcement materials relevant to field conditions, as well
as in the laboratory, will increase our knowledge of the
material behaviour. Resulting from these developments will
be refinements in the limit state analysis of reinforced soil,
particularly under serviceability conditions. The process of
codification and standardisation in reinforced soil is
underway, but a balance must be struck betweenpreserving
sufficient freedom for continued development of the
technology, while capturing present best practice in widely
accepted standards which will encourage further the
widespread application of reinforced soil throughout the
construction industry.
Reinforcement of the earth has been mostly to
reduce the total and differential settlement and has
improved the serviceability limit of structures founded on
the soft or compressible earth. The concept has facilitated
construction of the high to very high retaining walls and
slopes. The reinforcement of slopes can be achieved in a
variety of ways such as nailing, root piles,dowels,anchors or
even as a combination of reinforcement and drainage.

The concept of reinforcing earth has also attracted the
attention of the academic world, for although the concept is
easily graspedthetheoretical aspectsinvolvedare numerous
As a result, much research and development work has been
undertaken in universities and laboratories and earth
reinforcing is now recognized as a separate subject in its
own right in geotechnical field.
ACKNOWLEDGEMENT
I am highly indebted to my paper advisor Asst. Prof. Ankit
Laddha currently working at JIET group of institution,
jodhpur, Rajasthan, India and guide Prof. Dr. D.G.M. Purohit
and I express my deep sense of gratitude to him for guiding
and giving timely advice and suggestions in the successful
completion of the seminar. It was a matterofgreathonour to
have him as a guide in the preparation of this seminar.
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