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


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

Geo-synthetic Reinforced Pavements 4

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.


TYPES OF GEO-SYNTHETICS

The term is generally regarded to

encompass four main products,

Geo-textiles

Geo-nets/geo-grids

Geo-membranes

Geo-composites


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



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.


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



Geo-membranes

Impermeable sheets produced from

polymeric materials

Manufactured several ways, excluding

woven methods

Manufactured using fiberglass and

bitumen


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


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



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



GEO-SYNTHETIC

ADVANTAGES Space Savings

Material Quality Control

Construction Quality Control

Cost Savings

Technical Superiority

Construction Timing

Material Availability

Environmental Sensitivity


FUNCTIONS 1. Separation

2. Filtration, drainage

3. Reinforcement

4. Fluid Barrier

5. Protection


Bearing capacity

increase

Membrane tension

support

Lateral restraint

Separation


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


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


Reinforcement

Improves the performance of pavements by three possible mechanisms

1. Lateral restraint

2. Bearing capacity increase

3. Membrane tension support


Lateral Restraint

Lateral restraint of the base and sub-grade

through friction and interlock between the

aggregate, soil and the geo-synthetic


Lateral Restraint


Bearing Capacity Increase

Increase in the system BP by forcing the

potential BP failure surface to develop along

alternate, higher shear strength surfaces.


Bearing Capacity Increase


Membrane Tension

Support

A third possible geo-synthetic reinforcement

function is membrane-type support of wheel

loads


Membrane Tension Support


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.


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)


FUNCTIONS


FUNCTIONS


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


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.


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


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).


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).


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).


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).


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


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


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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84635279 Geosynthetic Reinforced Pavements