Geosynthetics for ground
improvement of Embankments
Various Functions of Geosynthetics
Sealing
Protection
Filtration
Separation
Drainage
Reinforcement
Important for Ground Improvement
Ground Improvement
Coastal Roads- Mumbai ,Vizag ,Cochin, Manglore , Kandla, Rann of Kutch etc
Peculiar Characteristics of Marine Land
•Soft ground - which is susceptible to failure or cause excessive settlement when
superstructure is constructed over it
• Marine soil mainly consists of Marine Saturated clays and fine silts ( alluvium),
 Loose very fine sand and silts( especially when submerged)
PROBLEMS in EMBANKMENTS
Problems associated with Construction of Embankments
on soft ground
•
Construction Material: Soft Soil
– Fine soil having very low undrained shear strength and plastic
– Very High Compressibility and moisture content varies from 60-100
– Very low permeability (10-5mm/sec - 10-8 mm/sec),
– Normally consolidated & insitu shear strength varies from 7-20 kPa.
– the failure happens at an undrained condition within a short period after
the embankment construction.
Slip instability
Embankment
Increased construction activities in coastal
Cities and harbors pose a challenging task to
engineers to meet the needs of rapid development
Soft foundation
Stability of an embankment in soft clay depends
on interaction of the following parameters.
•Height of embankment
•Base width of embankment
•‘Depth of soft clay
•Shear strength of soft clay
Failures can occur in embankemts of very low heights , say 1m to 1.5 m
, when clay is having poor shear strength and/or
Embankment is having very restricted base width
Failure modes
Bearing Capacity /Foundation Extrusiion
Lateral Sliding
Rotational Failure
Overall Failure
FAILURE PATTERNS
Failure patterns -Embankments on soft
soils :
• foundation soil failure
• slide of embankment fill on underlying
soft soil
• excess of displacement
APPLICATION OF GEOSYNTHETICS
FOR GROUND IMPROVEMENT
Geosynthetics reinforcement
A high strength and stiff reinforcement layer at the fill base
can be used in order to improve embankment stability
What can geosynthetics do?
to increase the safety-factors against
catastrophic failure
to limit the magnitude of overall settlements
to control differential settlements
YES
NO
PARTIALLY
Geosynthetics in Embankments
• More common and well known, well established solution
• Used as an alternative to conventional system
• Considered as cost-effective solution
• Basic Application includes:
Solutions using Geosynthetics
Basal reinforcement
Basal reinforcement
for Piled Embankments
PVDs
Stone Column
GROUND IMPROVEMENT
A. Concept of Basal Reinforcement
Embankment
Reinforcement
Drainage blanket (0.5 m crushed stone)
Anchorage
block
Working principle of Basal Reinforcement •Basal reinforcement is used to form a geosynthetic raft & transfers the load to
the soil directly, or
With sand piles, or
 With stone columns or piles,
 It enables to maximize the economic benefits of piles/ stone columns
installed in soft foundations by decreasing the diameter and increasing the
spacing. Pile cap dimensions can be optimised wihen Basal reinforcement is
utilised.
The reinforcement also counteracts the horizontal thrust of embankment fill
and need for raking piles along the extremities of the foundation can be
eliminated.
Contribution of Reinforcement for stability of Embankment
By placing a stiff reinforcement layer at the embankment base, improved
Safety Factors can be achieved for the following-
1. Rotation Stability of Embankment Fill
2. Sliding Stability of Embankment Fill
3. Overall Stability
4. Foundation Bearing/Extrusion Stability
Contribution of Reinforcement for stability of Embankment
–
The load in the reinforcement increases to a maximum
during construction.
–
As the foundation consolidates the reinforcement
carries less load
–
When the foundation has consolidated it carries all of
the embankment load - the reinforcement is no longer
required
Force in
reinforcement
Contribution of Reinforcement for stability of Embankment
End of construction
CU of soft soil
Time
Consolidation of soft soil
Time
Application of Geo synthetic as basal reinforcement along
with other techniques of ground improvement
CL
• Basal Reinforcement + Piles –
Gabion Thrust Block
Embankment Fill
Geosynthetic H
Pile Caps
Highly Compressible
Soft Soil
End Bearing Piles
Through Soft Material
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.
Basal Reinforcement+ Piles
CL
Gabion Thrust Block
Embankment Fill
Pile Caps
Highly Compressible
Soft Soil
End Bearing Piles
Through Soft Material
The pile and basal reinforcement technique
allows structures to be constructed to
required heights without any restraint on
construction rate with proper control of post
construction settlements
Geosynthetic H
Basal Reinforcement + Stone columns
•Basal Reinforcement + Stone columns–
The stone column technique, also known as vibro-replacement or vibrodisplacement, is a ground improvement process where vertical columns of
compacted aggregate are formed through the soils to be improved.
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.
Installation of Stone Column by Vibro-flotation
Basal Reinforcement + PVD
• Basal Reinforcement + PVD –
Ground improvement technique using prefabricated vertical drains PVD) is also a
suitable method to overcome the problem of excessive settlement in soft soils.
• PVD’s band shaped (rectangular
shaped) material consisting synthetic
geo textile jacket surrounding inner
plastic core.
• Jackets are of non woven polyester or
polypropylene geo textile.
Used in Embankment construction:
To accelerate settlements
To reduce time for consolidation
To avoid Post Construction Settlements
Principles of Ground Improvement Using PVD
 Horizontal/Radial Consolidation
• Use of preload (Pre-compression)
Resulting in
• Advancement of the expected settlements and reduction
in post construction settlements.
• Reduction in time required for consolidation.

Functioning of Drain
Functioning of Drain
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
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 drain
Field Installation
Advantages
Advantages of Using Basal 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
CASE STUDIES - Use of geo
synthetic Basal Reinforcement
for GROUND IMPROVEMENT
WORKS
Project: ROB FOR CONNECTIVITY BETWEEN MUNDRA AND NH8A,
MUNDRA , GUJRAT, INDIA
Problem: -
For ROB at Mundra in Gujarat, the solid approaches were retained using
Reinforced Soil (RS) Walls. The shear properties of existing soil were weak which
could have led to a major problem of bearing and global instability.
SOLUTIONIn order to achieve the required global and bearing stability, ground improvement
using basal reinforcement over piles and for lower heights basal reinforcement over
stone columns was proposed.
Site Conditions
Maximum Height of reinforced soil wall – 9 meter
Soil up to 3.0 meter was clayee silt which is followed by sand and silt
with traces of clay till 9.0 m.
Ground water table was up to 1.5 meter.
Basal Reinforcement selected :
High Strength Geogrids having monoaxial array of Geosynthetics strips , which has
a planar structure were used as basal reinforcement to improve the strength of the
underlying soil.
A summary of the solution is provided below:
Installation of drainage layer
Quality Aspects at site
Site preparation
Reinforcement storage
Placement of Reinforcement’
Reinforcement Jointing
End Anchorages
Fill considerations
Reinforcement is temporarily
secured in place with pins,
as required by fill properties.
Fill in the immediate contact
with reinforcement is placed and spread
in the longitudinal direction of
reinforcement only.
The unidirectional ultimate strength of the mono-axial geo grid was 200kN/m.
Stone columns were used to reduce the settlement of the approach road at higher
heights.
High strength geo synthetic used as basal reinforcement were effectively able to
distribute the stress uniformly to the foundation soil , thereby
decreasing the differential settlement.
Maximum tensile load was calculated as the sum of the load needed to transfer the
vertical embankment loading on the stone columns and the load needed
to resist lateral sliding.
The settlement of the soil in between the columns was also reduced considerably
since the load was transmitted to columns through basal reinforcement..
Concluding Remarks
• 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 act
as a Basal Reinforcement to improve stability of embankments
on Soft Soil.
THANKS FOR YOUR PRESENCE AND SUPPORT