Geosynthetics for Ground Improvement of Embankments on Soft

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GEOSYNTHETIC-REINFORCED EMBANKMENTS ON SOFT FOUNDATIONS

Presented by: K.Narendra 203114019

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Soft soil properties• Very High Compressibility and moisture content

varies from 60-100%

• Very low permeability (10-5 mm/sec - 10-8

mm/sec).

• Normally consolidated & in-situ shear strength

varies from 7-20 kPa.

• Fine soil having very low undrained shear

strength and plastic. In which failure occurs at

an undrained condition within a short period

after the embankment construction.

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Stability of an embankment on soft clay depends on the following parameters.

• Height of embankment• Base width of embankment• Depth of soft clay• Shear strength of soft clay Failures can occur in

embankments of very low heights say 1m to 1.5 m when clay is having poor shear strength or Embankment is having very restricted base width.

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Failure patterns

Embankments on soft soils :

• Foundation extrusion

• Rotational failure

• Lateral sliding

• Overall failure

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1. FOUNDATION EXTRUSION

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2. ROTATIONAL FAILURE

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3. LATERAL SLIDING

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4. OVERALL FAILURE

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APPLICATION OF GEOSYNTHETICS

FOR GROUND IMPROVEMENT

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Geosynthetic reinforcement

A high strength and stiff reinforcement layer at the fill base can be used in order to improve embankment stability.

Effects due to use of reinforcement layer:

• To increase the safety-factors against catastrophic failure.

• To control partially differential settlements.• It does not limit the magnitude of overall

settlements.

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Working principle

Reinforcement forms a geosynthetic raft &

transfers the load

the directly to the soil or

Indirectly through sand piles, stone

columns and pile foundations to deeper

soil.

The reinforcement also

counteracts the horizontal thrust of

embankment fill and need for raking piles

along the extremities of the foundation

can be eliminated.

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Contribution of Reinforcement for stability of Embankment

By placing a stiff reinforcement layer at the embankment base, Safety Factors for the following types of failures can be improved

1. Foundation Bearing/Extrusion Stability

2. Rotation Stability of Embankment Fill3. Sliding Stability of Embankment Fill4. Overall Stability

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• Time

•Fo

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in•

rein

forc

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End of construction

• The load in the reinforcement increases to a maximum value during construction.

• As the foundation is undergoing consolidation, the load transfers from reinforcement to foundation.

• When the foundation has consolidated it carries all of the embankment load ,the reinforcement is no longer required.

Consolidation of soft soil

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Geo synthetic reinforcement along with other techniques of ground improvement

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1. GEOTEXTILE REINFORCEMENT + PILES

End Bearing PilesThrough Soft Material

Pile Caps

Highly CompressibleSoft Soil

Embankment FillGabion Thrust BlockGeosynthetic

CL

H

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REINFORCEMENT LAYER+PILE FOUNDATION

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Pile foundations are used to carry and transfer the

load of the structure to the bearing ground located

at more depth below ground surface.

So they are used in such cases where the

foundation soil is not able to take the structure

load at all and ground improvement is either not

possible or is more expensive than pile

foundations.

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2. Reinforcement layer+ Stone columns

The stone column technique also known as

vibro-replacement or vibro-displacement.

These columns result in increased vertical

load carrying capacity and improved shear

resistance in the soil mass.

For soils with appreciable silt or clay

content that do not respond to deep

vibratory compaction it is advantageous to

create stiff reinforcing elements in the soil

mass.

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REINFORCEMENT LAYER +STONE COLUMNS

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3.GEOTEXTILE REINFORCEMENT+ PVD

• PVD’s band shaped (rectangular shaped) material consisting synthetic geotextile jacket surrounding inner plastic core.

• Jackets are of non woven polyester or polypropylene

geotextile.Functions of filter jacket• To prevent soil particles and allow water to

flow in• To provide the cover to internal drain flow

i.e. function of filter jacket mainly filtration, to some extent separation

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Functions of the core:• To provide internal flow path for water

along the drain• To provide support to filter jacket• To provide the resistance to longitudinal

stretching as well as buckling of the drainEffects:

• To accelerate settlements i.e

advancement of the expected

settlements

• To reduce time for consolidation

• To avoid Post Construction Settlements

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REINFORCEMENT LAYER + PVD

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Advantages of Using Geosynthetic Reinforcement for Ground Improvement

• Easy and Rapid construction is possible

over weak soil

• Improved load carrying capacity

• Better drainage arrangement can be

Provided

• Cost effective if compared to conventional

solution

• Differential settlement can be controlled

• Chemically inactive, non biodegradable

material hence high durability

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Conclusion

• Construction of embankments on soft soil can be critical because of they have low strength & high compressibility.

• Reinforcement material can be placed at foundation level to improve stability of embankments on Soft Soil.

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THANK YOU