GEOSYNTHETIC – REINFORCED PAVEMENTS

8/2/2019 GEOSYNTHETIC REINFORCED PAVEMENTS

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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

2Geo-synthetic Reinforced Pavements


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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


Bearing capacityincrease

Membrane tension

support

Lateral restraint


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Separation


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


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


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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GEOSYNTHETIC – REINFORCED PAVEMENTS