0ground Improvement Techniques

7/30/2019 0ground Improvement Techniques

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BY

S.DHARMA RAJU 09241A0108


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INTRODUCTION

o Need for Ground Improvement. Swelling and shrinkage

Collapsible soils.

Soft soils. Sands and gravelly deposits.

Foundations on dumps and

sanitary landfills.

Organic and peaty soils.


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1. Soil stabilization

2. Vertical drains

3. Stabilization trenches

4.

Soil nailing5. Stone columns

6. Vibro compaction

7. Dynamic compaction


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Improvement of stability or bearing capacity of

soil by use of controlled compaction or by the

addition of suitable admixtures or stabilizers.

Soil stabilisation is alteration of any property of

soil to improve its engineering performance.


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To increase or decrease strength. To increase or decrease permeability.

To reduse compressibility.

soil stabilization has beensuccessfully used in all types of engineeringproblems but its most common application isthe strengthening of highway and airport

pavements.+


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o The methods of soil stabilization are:

1. Mechanical Stabilization

2. Soil-cement Stabilization

3. Soil-lime Stabilization

4. Soil-bitumen Stabilization

5. Chemical Stabilization

6. Electrical Stabilization7. Stabilization by geotextile

8. Using bio-enzymes


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o Mechanical Stabilization

Process of improving the properties of soil bychanging its gradation or rearragement of soil

particles.

o Cement Stabilization

Done by mixing soil and cement with water andcompacting the mix to attain a strong material.

o Lime Stabilization Lime stabilization is done by adding lime

(5%-10%) to soil. Lime decreases soil density and increases soil

strength.


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o Bituminous Stabilization

Bituminous stabilization provide water proofing

and binding.Bituminous materials such as asphalts,cut

backs,emulsions and tar.

o Chemical Stabilization

Stabilizationby adding different chemicals .

o Electrical Stabilization

Done by a process known as electro-osmosis.


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o Stabilization by Geotextiles

Geotextile which have very high tensile strength

can be used as reinforcement for strengtheningsoil.

o Stabilization using Bio-Enzymes

Bio-enzyme stabilization is a newer technique

for strengthening of sub grade soil.

Terra Zyme is one of the largely usedbio enzymes.


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These act as free draining water channelsurrounded by a thin filter jacket whichprevents the surrounding soil entering to thecore.

A vertical sand drain accelerates the rate ofconsolidation.

Installation of vertical sand drains is aconvenient technique for stabilization of softand compressible soil .


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o There are two types of vertical drains

sand drains and sand wicks.


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oSand drains Typically 200-500 mm in dia.

Formed by infilling sand in to a hole in the ground. Hole formed by driving ,jetting .

Typical spacing 1.5 - 6.0 m.

oSand wicks Sand wicks are improved technique of sand drains.

A small diameter hole is made by boring.


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Excavation which has a blanket of filter materialbetween 0.5m and 1.0 m thick against its

upstream slope and at the bottom of system for

collecting and eliminating water.

Improves the stability of embankment by

providing drainage and replacing weaker

material with better material .


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Earth retention structure that combinesreinforcements and shortcrete to support

excavations, hillside, embankment steeping

etc

The nails must have bending stress. The tension

developed in nails provides resisting forces

which stabilize the soil mass.


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o SoilNailing


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Done to provide adequate support for relatively

light foundation.

The method consists of forming vertical holes in

ground which are filled with compacted crushed

stone, gravel and sand or a mixture.

stone columns


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For loose sand deposits, the density index canbe increased by vibro compaction.

This process employs a depth vibrator

suspended from crane.

Compaction of sand can be achieved up to

distance of 2.5m from axis of vibrator.

Compaction can be carried out to significantdepths up to 12m.


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Vibro-compaction

oVibro-compaction


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This involves in increasing the density of soilnear the surface by tamping.

Density improvement up to 10m is feasible.

This method consists of dropping heavy mass of

8 to 40 tonnes known as pounder on the surface

from a height 5 to 30m


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Dynamiccompaction

Dynamic compaction

Equipment


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Ground improvement techniques have beenextensively used depending up on type and

soils.

Lime stabilization is suitable for expansive soil like blackcotton soils.

In bitumen stabilization optimum content of bitumenfrom 4 to 6 % soil.

Electrical and Chemical stabilization are expensive

to others.

Stabilization by grouting is suitable only for soils withpermeability.


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Stabilization by Terra Zyme is most effective for finegrained soil.

Provision of capillary cut-off is effective forexpansive soils.

For soft and compressible soils provision of sanddrains and sand wicks are found to be effective.

Dynamic compaction is found suitable for soft, loosecohesionless soil layers..

Stone column has also been found useful for softsoils.


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0ground Improvement Techniques