84635279 Geosynthetic Reinforced Pavements

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Overview of The

Presentation Scope of geo-synthetics

What are geo-synthetics

Types of geo-synthetics

Geo-synthetic Advantages

Functions

Sub-grade conditions in which geosynthetics are useful

Potential geo-synthetic benefits

Conclusions

2 Geo-synthetic Reinforced Pavements

SCOPE OF GEO-

SYNTHETICS

Limited financial resources

Requirement of high- quality materials

Unavailability or short in supply

3 Geo-synthetic Reinforced Pavements

WHAT ARE GEO-

SYNTHETICS..?

A range of generally synthetic products

used to solve geotechnical problems.

The synthetic nature make them suitable

for 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 material

used with soil, rock, earth, or other

geotechnical-related material as an

integral part of a civil engineering

project, structure, or system.

5 Geo-synthetic Reinforced Pavements

TYPES OF GEO-SYNTHETICS

The term is generally regarded to

encompass four main products,

Geo-textiles

Geo-nets/geo-grids

Geo-membranes

Geo-composites

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Geo-textiles

Manufactured from mainly polymeric yarns

and fibers, consisting primarily of

polypropylene, polyester, polyethylene and

polyamide

Woven - interlacing of yarns

Non-woven - by various methods other than

weaving, mainly heat bonded, needle

punched and chemically bonded

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Geo-nets/geo-grids

Stiffer than geo-textiles and have relatively

large voids within the material

Production include bonding or interlacing.

Produced from nearly all polymeric

materials.

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Geo-nets/geo-grids

Geogrids are meshes of a regular pattern

of tensile elements usually made of a

fairly rigid type of plastic

They provide increased shear strength

between soil strata interfaces

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Geo-membranes

Impermeable sheets produced from

polymeric materials

Manufactured several ways, excluding

woven 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 their

leachates

Acts as an escape route for gases and

leachates generated in wastes

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Made of various materials including low

density polyethylene, high density

polyethylene, polyvinyl chloride and

polypropylene

PVC geo-membranes are very flexible and

can conform to uneven surfaces without

being punctured

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Geo-composites

Geosynthetics which are

a combination of any of the above three

A geo-net sandwiched between two non-woven geo-textile layers can be used to provide a drainage layer with high transmissivity

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GEO-SYNTHETIC

ADVANTAGES 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. Reinforcement

4. Fluid Barrier

5. Protection

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Bearing capacity

increase

Membrane tension

support

Lateral restraint

Separation

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Geo-synthetics is placed at the interface

between the aggregate base course and

the sub-grade.

Functions as a separator to prevent two

dissimilar materials (sub-grade soil and

aggregates) from intermixing.

Separation

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Filtration, Drainage

Geo-textile act as a filter to prevent fines

from migrating up in to the aggregate

due to high pore water pressures

Acts as a drain, allowing the excess

pore water pressures to dissipate

through the geo-textiles

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Reinforcement

Improves the performance of pavements by three 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-grade

through 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 the

potential 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 wheel

loads

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Membrane Tension Support

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Fluid Barrier

Geo-membranes, thin-film geo-textile

composites, are used as fluid barriers to

impede the flow of a liquid or gas one

location to another.

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Protection

The geo-synthetic acts as a stress relief

layer.

Geo-synthetic blankets and geo-synthetic

mats reduce erosion caused by rainfall

impact.

Nonwoven geo-textiles is often used to

prevent puncture of geo-membranes (by

reducing point stresses)

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FUNCTIONS

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FUNCTIONS

Geo-synthetic Reinforced Pavements 33

SUBGRADE CONDITIONS IN

WHICH GEO-SYNTHETICS

ARE

USEFUL

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

WHICH GEO-SYNTHETICS

ARE

USEFUL

High water table

High sensitivity

Under these conditions, geosynthetics function primarily as separators and filters to stabilize the sub-grade.

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FUNCTIONS

Un drained Shear

Strength (kPa)

Sub-grade CBR

Functions

60 – 90

2 - 3

Filtration and possibly

separation

30 - 60

1 - 2

Filtration, separation,

and

possibly reinforcement

< 30

< 1

All 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 or

otherwise 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: separation

and reinforcement).

Reduces disturbance of the sub-grade during

construction. (Function: separation and

reinforcement).

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Allows an increase in sub-grade strength

over time. (Function: filtration).

Reduces the differential settlement of the

roadway, this helps in maintain pavement

integrity and uniformity. (Function:

reinforcement).

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Reduces the depth of excavation required

for the removal of unsuitable sub-grade

materials (Function: separation and

reinforcement).

Reduces maintenance and extends the life

of the pavement. (Functions: all).

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CONCLUSIONS

Geo-synthetic reinforcement in pavement

design and construction should be

widespread.

Geo-synthetic reinforcements are

incorporated into permanent, paved roads

either as base (or sub-base) reinforcement

As sub-grade restraint for construction of

flexible or rigid roadways over weak sub-

grade conditions

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REFERANCES

1. Engineering properties of sand fiber mixtures

for road construction by Rosa L. et al, Journal

of geotechnical and geo-environmental engg.

March 2001

2. Performance of geo-synthetic reinforced

asphalt 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 aggregate

base/sub-base courses of pavement

structures 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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