geosynthetics for ground improvement of embankments on soft
TRANSCRIPT
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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
rce
in•
rein
forc
emen
t
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