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SEMINAR ON
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Overview of ThePresentation
Scope of geo-synthetics
What are geo-synthetics
Types of geo-synthetics
Geo-synthetic Advantages Functions
Sub-grade conditions in whichgeosynthetics are useful
Potential geo-synthetic benefits
Conclusions
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SCOPE OF GEO-SYNTHETICS
Limited financial resources
Requirement of high- quality materials
Unavailability or short in supply
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WHAT ARE GEO-
SYNTHETICS..? A range of generally synthetic products
used to solve geotechnical problems.
The synthetic nature make them suitablefor use in the ground where high levels
of durability are required
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WHAT ARE GEO-
SYNTHETICS..? ASTM (1997) has defined a geo-
synthetic as a planar product
manufactured from a polymeric materialused with soil, rock, earth, or othergeotechnical-related material as anintegral part of a civil engineeringproject, structure, or system.
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TYPES OF GEO-SYNTHETICS
The term is generally regarded toencompass four main products,
Geo-textiles
Geo-nets/geo-grids
Geo-membranes
Geo-composites
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Geo-textiles
Manufactured from mainly polymeric yarnsand fibers, consisting primarily ofpolypropylene, polyester, polyethylene and
polyamide
Woven - interlacing of yarns
Non-woven - by various methods other thanweaving, mainly heat bonded, needlepunched and chemically bonded
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Geo-nets/geo-grids
Stiffer than geo-textiles and have relativelylarge voids within the material
Production include bonding or interlacing.
Produced from nearly all polymericmaterials.
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Geo-nets/geo-grids
Geogrids are meshes of a regular patternof tensile elements usually made of a
fairly rigid type of plastic
They provide increased shear strengthbetween soil strata interfaces
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Geo-membranes
Impermeable sheets produced frompolymeric materials
Manufactured several ways, excludingwoven methods
Manufactured using fiberglass and
bitumen
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Used widely as cut-offs and liners
Applied largely is the containment of
hazardous and municipal wastes and theirleachates
Acts as an escape route for gases andleachates generated in wastes
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Made of various materials including lowdensity polyethylene, high densitypolyethylene, polyvinyl chloride and
polypropylene
PVC geo-membranes are very flexible and
can conform to uneven surfaces withoutbeing punctured
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Geo-composites
Geosynthetics which area combination of any ofthe above three
A geo-net sandwichedbetween two non-wovengeo-textile layers can be
used to provide adrainage layer with hightransmissivity
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GEO-SYNTHETICADVANTAGES
Space Savings
Material Quality Control
Construction Quality Control
Cost Savings
Technical Superiority
Construction Timing
Material Availability
Environmental Sensitivity
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FUNCTIONS
1. Separation
2. Filtration, drainage
3. Reinforcement4. Fluid Barrier
5. Protection
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Bearing capacityincrease
Membrane tension
support
Lateral restraint
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Separation
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Geo-synthetics is placed at the interfacebetween the aggregate base course andthe sub-grade.
Functions as a separator to prevent twodissimilar materials (sub-grade soil and
aggregates) from intermixing.
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Separation
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Filtration, Drainage
Geo-textile act as a filter to prevent finesfrom migrating up in to the aggregatedue to high pore water pressures
Acts as a drain, allowing the excess
pore water pressures to dissipatethrough the geo-textiles
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Reinforcement
Improves the performance of pavements bythree possible mechanisms
1. Lateral restraint
2. Bearing capacity increase
3. Membrane tension support
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Lateral Restraint
Lateral restraint of the base and sub-gradethrough friction and interlock between the
aggregate, soil and the geo-synthetic
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Lateral Restraint
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Bearing Capacity Increase
Increase in the system BP by forcing thepotential BP failure surface to develop along
alternate, higher shear strength surfaces.
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Bearing Capacity Increase
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Membrane Tension
Support
A third possible geo-synthetic reinforcement
function is membrane-type support of wheelloads
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Membrane Tension Support
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Fluid Barrier
Geo-membranes, thin-film geo-textilecomposites, are used as fluid barriers toimpede the flow of a liquid or gas onelocation to another.
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Protection
The geo-synthetic acts as a stress relieflayer.
Geo-synthetic blankets and geo-synthetic
mats reduce erosion caused by rainfallimpact.
Nonwoven geo-textiles is often used to
prevent puncture of geo-membranes (byreducing point stresses)
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FUNCTIONS
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FUNCTIONS
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O O
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SUBGRADE CONDITIONS INWHICH GEO-SYNTHETICS
AREUSEFUL
Poor soils
(SC, CL, CH, ML, MH, OL, OH, and PT)
Low un-drained shear strength
Cu< 90 kPa
CBR < 3
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SUBGRADE CONDITIONS IN
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SUBGRADE CONDITIONS INWHICH GEO-SYNTHETICS
AREUSEFUL
High water table
High sensitivity
Under these conditions, geosyntheticsfunction primarily as separators and filtersto stabilize the sub-grade.
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FUNCTIONS
Un drained ShearStrength (kPa)
Sub-grade CBR Functions
60
90 2 - 3
Filtration and possibly
separation
30 - 60 1 - 2Filtration, separation,
andpossibly reinforcement
< 30 < 1All functions, including
reinforcement
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POTENTIAL GEO-SYNTHETIC BENEFITS
Reduces the intensity of stress on the sub-grade and prevents the base aggregate from
penetrating in to the sub-grade. (Function:separation).
Prevents sub-grade fines from pumping orotherwise migrating up in to the base.(Function: separation and filtration).
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Prevents contamination of the base materials.(Function: filtration).
Reduces the thickness of aggregate required to
stabilize the sub-grade. (Function: separationand reinforcement).
Reduces disturbance of the sub-grade duringconstruction. (Function: separation andreinforcement).
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Allows an increase in sub-grade strengthover time. (Function: filtration).
Reduces the differential settlement of theroadway, this helps in maintain pavementintegrity and uniformity. (Function:
reinforcement).
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Reduces the depth of excavation requiredfor the removal of unsuitable sub-gradematerials (Function: separation and
reinforcement).
Reduces maintenance and extends the life
of the pavement. (Functions: all).
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CONCLUSIONS
Geo-synthetic reinforcement in pavementdesign and construction should bewidespread.
Geo-synthetic reinforcements areincorporated into permanent, paved roadseither as base (or sub-base) reinforcement
As sub-grade restraint for construction offlexible or rigid roadways over weak sub-grade conditions
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REFERANCES
1. Engineering properties of sand fiber mixturesfor road construction by Rosa L. et al, Journalof geotechnical and geo-environmental engg.
March 2001
2. Performance of geo-synthetic reinforcedasphalt pavements by Hoe I Ling et al, Journal
of geotechnical and geo-environmental engg.February 2001
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3. Geo-synthetic reinforcement of aggregatebase/sub-base courses of pavementstructures GMA White paper II June 27, 2000
4. Experimental analysis of geo-textiles & geo-fibers composites, by Dr A. K. Haghi
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