GROUND IMPROVEMENT TECHNIQUES

GROUND IMPROVEMENT TECHNIQUES

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  GROUND IMPROVEMENT TECHNIQUES Presented By A HARSHITHA AssistantProfessor CIVIL DEPARTMENT AVNIET
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  Foreword  Engineering GroundModifications {Intro}  Need and Objectives  Identification of soil types  In-situ and laboratory test  Characterization of problematic soils  Methods and Their applications
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  Intro Ground improvement maybe defined as “The process in which in-situ soils are improved for the support of the foundations in known as ground improvement”. • In the early times before the advancement in the geotechnical engineering, the only chance for the foundation engineers was to design the foundation matching to the sub soil conditions at the provided site. But now a day due to the improvements in geotechnical techniques and with the help of latest technology it is possible for us to modify the weak foundation soil to the strength and compressibility characteristics to suit the foundation of our choice. • Ground Improvement is the application of various geotechnical techniques that are used to re- engineer existing soils to improve their engineering characteristics.
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  Needs of GIT: Asmore and more land becomes subject to urban or industrial development, good construction sites and borrow areas are difficult to find and the soil improvement alternatives becomes the best option, technically and economically. Where a project encounters difficult foundation conditions, possible alternative solutions are: Avoid the particular site. Relocate a planned highway or development site. Design the planned structure accordingly Remove and replace unsuitable soils. Removing organic topsoil, which is soft, compressible, and volumetrically unstable. This is a standard precaution in road or foundation construction.
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  Objective of GIT Themost common traditional objectives include improvement of the soil and ground for use as a foundation or construction material. The typical Engineering objectives have been Increasing shear strength, durability, stiffness, stability. Mitigating undesirable properties (eg . Shrink/ swell potential, compressibility, liquefability.) Modifying permeability, the rate of fluid to flow through a medium. Ground improvement methods have provided adverse choice of approaches to solving these challenges.
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  Factors affecting choiceof improvement method: SOIL TYPE AREA REQUIRED SOIL PROPERTIES AVAILABILITY OF MATERIALS AVAILABILITY OF SKILLS ENVIRONMENTAL CONCERNS ECONOMICS
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  Identifying your soiltype • Pick up a handful and squeeze it together. Sand feels gritty and the grains do not stick together when squeezed. Loam feels velvety or flour-like when dry and forms a weak ball shape when wet which crumbles apart when dry. Clay feels sticky, but goes smooth when rubbed. Chalk will have large lumps in it and be hard to mould.
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  TYPES OF SOILS •Claysoil •Sandy soil •Chalky •Slit soil •Loam soil
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  In-situ laboratory testfor problematic Soils • In Situ and Laboratory Testing ESG’s (Environmental, Social and Governance) geotechnical division offers a wide range of in situ and laboratory-based testing methods for the measurement of soil and rock stiffness parameters. • Various Lab Test on Soil inspection or say geotechnical inspection is very important in understanding the physical properties of soil and the rocks beneath. This is required to ascertain the type of foundation required for the proposed construction. Various tests are done to explore the sub surface and surface characteristics of soil .Some of these are given below. Just click on the link to go to the details of that particular test. • Standard penetration test • Cone penetration test • Density of soil by sand replacement method and core cutter method • Grain size analysis
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  Laboratory Tests Water content Plastic limitof soil Free swelling of soil Liquid limit of soil Particle size distribution of soil The specific gravity of soil
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  Classification of GroundModification Techniques Four groups of ground improvement Techniques are distinguished:
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  Mechanical modification • Soildensity is increased by the application of Short-term external mechanical forces, including Compaction of surface layers by • Static • Vibratory • Impact rollers • Plate vibrators.
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  Hydraulic modification:-Free –porewater is forced out of the soil via (by means of) drains of wells. - In coarse grained soils, this is achieved by lowering the ground water level through pumping from boreholes or trenches. - In fine-grained soils, The long term application of external loads (preloading) or electrical forces (electrokinetic stabilization) is required. Physical and Chemical modification:- Additives include: - natural soils - industrial by- products or waste materials (fly ash, slag), - Cementations and other chemicals (lime, cement) which react with each other and the ground. When additives are injected via boreholes under pressure into the voids within the ground or between it and a structure, the process is called GROUTING. THERMAL METHODS OF MODIFICATION. Rigs with multiple injectors deliver the stabilizing fluid into the soil. The fluid will prefer to travel into cracks and fissures. Soil stabilization by heating the ground and by freezing the ground.
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  Modification by inclusionand Confinement Reinforcement Strips Fibers Bars Meshes and Fabrics. Insitu reinforcement is achieved by nails and anchors.