A SEMINAR REPORT ON

ARTIFICIAL GEOTEXTILE

AS A PAVEMENT MATERIAL

J ABHINAV NAIK (141807)

M.Tech I year, Geotechnical division,

NIT Warangal.

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INTRODUCTION

In the early 1960s and 1970s, some pioneering engineers

wondered if textiles could be used to control soils under

difficult conditions. For example, very wet soils need draining

and textiles were used to line drains, to prevent mud and silt

from clogging up the drains. Similarly, engineers tried to use

textiles beneath small access roads constructed over very soft

wet soils. It was found that these textiles helped to increase

the life and performance of roads. Also, early work was being

undertaken in the laying of textiles on the coast to prevent

erosion by wave action.

In 1977 Rankilor produced what was probably the first

‘design’ manual for a commercial product and this was followed by

a textbook written in 1980 which built on the extensive

experience that had been amassed by this time. As is so typical

of scientific development, many engineers were soon working

worldwide on the development of geotextiles. During the last 20

years of the 20th century, the use of geotextiles spread

geographically worldwide and in area terms their use increased

almost exponentially.Much confusion is evident throughout typical

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design sources regarding geotextiles themselves as well as

applications relevant to roadway design.

A geotextile is defined as a permeable geosynthetic made of

textile materials. Among the different geosynthetic products,

geotextiles present the widest range of properties and can be

used for the widest variety of transportation applications.

A permeable geosynthetic comprised solely of textiles.

Geotextiles are used with foundation, soil, rock, earth, or any other

geotechnical engineering-related material as an integral part of a

human-made product structure, or system. Due to the very wide range

of applications and the tremendous variety of available textiles

having widely different properties, the selection of a particular

design method or design philosophy is a critical decision that

must be made before the actual mechanics of the design process

are initiated.

Manufacture of Geotextiles:

The polymers used in the manufacture of geotextile fibers

include the following, listed in order of decreasing use:

1. Polypropylene (85%)

2. Polyester (12%)

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3. Polyethylene (2%)

4. Polyamide (1%).

The most common types of filaments used in the manufacture

of geotextiles include monofilament, multifilament, staple

filament, and slit-film.

If fibers are twisted or spun together, they are known as a

yarn. The filaments, fibers, or yarns are formed into geotextiles

using either woven or nonwoven methods. Woven geotextiles are

manufactured using traditional weaving methods and a variety of

weave types: plain weave, basket weave, twill weave, and satin

weave.

Nonwoven geotextiles are manufactured by placing and

orienting the filaments or fibers onto a conveyor belt, which are

subsequently bonded by needle punching or by melt bonding. The

nonwoven geotextiles have tremendously different engineering

properties than the woven geotextiles. The type of polymer will

also influence significantly the engineering properties of these

products.

Common terminology associated with geotextiles includes

machine direction, cross machine direction, and selvage. Machine

direction refers to the direction in the plane of the fabric in

line with the direction of manufacture. Conversely, cross machine

direction refers to the direction in the plane of fabric

perpendicular to the direction of manufacture. The selvage is the

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finished area on the sides of the geotextile width that prevents

the yarns from unraveling.

Geotextile types:

Geotextiles basically fall into five categories

Woven Geotextles

Heat-bonded nonwoven Geotextles

Needlepunched nonwoven Geotextles

Knitted Geotextles

Woven fabrics are made on looms which impart a regular

rectilinear construction to them, but which can vary in terms of

the component fibres and the weave construction. They have a

surprisingly wide range of applications and they are used in

lighter weight form as soil separators, filters and erosion

control textiles. In heavy weights, they are used for soil

reinforcement in steep embankments and vertical soil walls; the

heavier weight products also tend to be used for the support of

embankments built over soft soils. The beneficial property of the

woven structure in terms of reinforcement, is that stress can be

absorbed by the warp and weft yarns and hence by fibres, without

much mechanical elongation. This gives them a relatively high

modulus or stiffness.

Heat-bonded nonwoven textiles are generally made from

continuous filament fine fibres that have been laid randomly onto

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a moving belt and passed between heated roller systems. These

fabrics acquire their coherence and strength from the partial

melting of fibres between the hot rollers, resulting in the

formation of a relatively thin sheet of textile.

Needlepunched nonwoven fabrics are made from blended webs of

continuous or staple filaments that are passed through banks of

multiple reciprocating barbed needles. The fabrics derive

mechanical coherence from the entangling of fibres caused by the

barbs on the reciprocating needles; these fabrics thus resemble

wool felts.

In the case of needlepunched textiles, considerable

thicknesses (up to more than 10 mm) and weights greater than

2000g m-2 can be achieved, whereas the heatbonding process is

limited in its efficacy as thickness increases. If sufficient

heat is applied to melt the internal fibres of a thick fabric

adequately, then the outer fibres will tend to be overheated and

overmelted. Conversely, if appropriate heat is applied to the

external fibres, then insufficient heat may be applied to the

centre of the sheet, resulting in inadequate bonding and

potential delamination in use.

Knitted fabrics, as used in the field of geotextiles, are

restricted to warp-knitted textiles, generally specially produced

for the purpose. Warp-knitting machines can produce fine filter

fabrics, medium meshes and large diameter soil reinforcing grids.

However, it is generally found that only the high strength end of

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the product range is cost effective, usually for soil

reinforcement and embankment support functions.

Geotextile Functions and Mechanisms :

An overview of geotextiles, alluded to many applications

falling into categories:

Separation

Reinforcement

Filtration

Drainage

Separartion:

Separation is defined as, “The introduction of a flexible

porous textile placed between dissimilar materials so that the

integrity and the functioning of both the materials can remain

intact or be improved”. In transportation applications

separation refers to the geotextile’s role in preventing the

intermixing of two adjacent soils. For example, by separating

fine subgrade soil from the aggregates of the base course, the

geotextile reserves the drainage and the strength

characteristics of the aggregate material.

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Applications in Pavements:

Between subgrade and stone base in paved roads and airfields

Between landfills and stone base courses

Between geomembranes and soil drainage layers

Between foundation and embankment soils for surcharge loads

Between foundation and embankment soils for roadway fills

Between foundation and encapsulated soil layers

Between foundation soils and rigid retaining walls

Between slopes and downstream stability berms

Beneath precast blocks and panels for aesthetic paving e.g.

hardscaping

Between drainage layers in poorly graded filter blankets

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Desi

gned

Thi

ckness

Between old and new asphalt layers

Reinforcement:

Reinforcement is the synergistic improvement in pavement

strength created by the introduction of a geotextile into a

pavement layer. While the function of reinforcement in the U.S.

has often been fulfilled by geogrids, geotextiles have been used

extensively as reinforcement inclusions, particularly overseas,

in transportation applications. The reinforcement function can be

developed primarily through the following three mechanisms

1. Lateral restraint through interfacial friction between

geotextile and soil/aggregate. When an aggregate layer is

subjected to traffic loading, the aggregate tends to move

laterally unless it is restrained by the subgrade or geosynthetic

reinforcement. Soft, weak subgrade soils provide very little

lateral restraint, so rutting develops when the aggregate moves

laterally. A geotextile with good frictional capabilities can

provide tensile resistance to lateral aggregate movement.

2. Increased bearing capacity, i.e., by forcing the potential

bearing surface failure plane to develop at alternate higher

shear strength surface.

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3. Membrane type of support of the wheel loads.

Applications:

To reinforce embankments

To aid in construction of steep slopes

As basal reinforcement over soft soils

To bridge over cracked or jointed rock

To create more stable side slopes due to high frictional

resistance

Filteration:

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It is defined as “the equilibrium geotextile-to-soil system

that allows for adequate liquid flow with limited soil loss

across the plane of the geotextile over a service lifetime

compatible with the application under consideration . To perform

this function the geotextile needs to satisfy two conflicting

requirements: the filter’s pore size must be small enough to

retain fine soil particles while the geotextile should permit

relatively unimpeded flow of water into the drainage media. A

common application illustrating the filtration function is the

use of a geotextile in a pavement edge drain.

Applications:

Beneath stone base for paved roads and airfields

Around crushed stone surrounding under drains

Around perforated under drain pipe

As a flexible form for restoring scoured bridge pier bearing

capacity

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Subgrade

Between backfill soil and weep holes in retaining walls

Between backfill soil and gabions

As a filter beneath precast blocks

Drainage:

In this function, the liquids especially Water is carried or

transmitted with in the plane of the Geotextile itself. This is

distinct from the filtration where the liquid flow across the

plane of the Geotextile. This is associated with the composite

Geotextiles that are used as a part in the drainage. The

hydraulic properties of Geotextiles is designed to drain excess

water off the construction - not by passing through the fabric -

but by flowing in the plane of the fabric away from the

construction. The use of a drainage geotextile ensures an ongoing

drainage of fluids with minimum pressure loss.

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Installation:

Proper installation of geotextile fabric with gravel, soil,

or other earthen material as a topcoat is best accomplished when

the soil at the site is dry. The following is a series of tips to

ensure proper site preparation, geotextile fabric installation,

and cover material application at the site. The first step,

however, is to select the proper geotextile fabric for the

application.

Clear the area of any sharp objects, stumps, and debris.

Grade the existing soil surface to provide adequate, but not

excessive, surface drainage.

Unroll the geotextile fabric over the application area. On a

windy day, the fabric will need to be secured with pins,

sod, stones, etc.

Place the gravel on the fabric. It is best to back dump when

unloading and spreading the gravel on the fabric with a

truck. Then complete the final spreading and smoothing with

earthmoving equipment like a dozer, front-end loader, skid

loader, or scraper.

Care should be taken when backfilling and compacting the

gravel. Geotextile fabric is tough, so it can be driven on.

However, truck tires may pull the fabric, causing it to

wrinkle. This condition may affect the proper installation

and performance of the system since less area may actually

be covered by the fabric.

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If it is necessary to overlap the fabric in order to cover a

larger area, a minimum of a one foot overlap is required for

proper use. In order to ensure a minimum of one foot of

overlay after the placement of the gravel or other topcoat,

it is recommended that the fabric be laid out with a two-

foot overlap before placing the gravel on the fabric. Once

placed, the gravel should be spread in the same direction as

the geotextile fabric overlap to avoid separation between

the two pieces of fabric. Staples are available to help hold

the fabric in place.

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Compact the gravel using earthmoving equipment, a tractor,

or farm trucks

.

Environmental Effects:

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There are four major environmental applications of

Geotextiles. They include,

1) Soil conservation

2) Protection

3) Bio-Barrier

4) Barrier

Soil conservation is an important application of

Geotextiles. The point of soil conservation is mainly used in the

slopes. In the area of slope stabilization, geogrids are used. In

an embankment fill or reduce the amount of movement possible,

keeping the fill in place. Very often the Geogrid is used as an

anchor, providing a reaction against the disturbing movement.

They are often used in the repairing of small slides in

engineering earth work. The area where the failure has occurred

is filled with the appropriate material and the Geogrid

reinforcement is pulled across it the failure surface now remains

intact and the slope is stabilized.

A protection membrane created using Geotextile materials

consisting of several layers of soil compacted between layers of

Geotextiles known technically as remembrances. This membrane must

be protected from puncture both during construction and after the

facility is placed service. The ability of a Geotextile to

protect the geomembrane from puncture is more a function of its

strength and thickness.

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Bio-Barrier is the cover section exposed to the sections of

the roots from plants require prevention of cover soil erosion.

Such penetration remains the most critical challenge to the long-

term integrids of cover systems. The product has a limited life

expectance. It is a function of moisture in the contact soil and

also it is quite expensive.

Geosynthetic lay liners were developed to waterproof

building basements and for lining of landscaping ponds. GCLs are

made by bonding bentonite granules between layers of Geotextiles.

The bonding can be performed by sand wiching the bentonite

granules between tow non-woven materials and then needling the

layers or by the use of water based adhesive to bond bentonite

between the two Geotextile layers

Advantages

When using geotextiles between different

construction layers, mixing of the layers is avoided,resulting in

an increase of bearing capacity andthereby also time and material

savings.

Highwater fl ow and good fi lter properties combinedwith the

necessary mechanical properties of thegeotextile ensure that fi

ne-grained particles areretained, while free movement of water is

maintained.

Consequently, stability is improved and life of theentire

construction is prolonged.

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Conclusion:

The majority of applications that call for the use of

geosynthetics require the products to perform for a minimum

expected time, commonly referred to as the design life. The rate

degradation of geosynthetics used must be such that the required

properties time to failure exceeds the requirements of the

design. The available properties must exceed the required

properties for the duration of the design. From the guidelines

published by CEN and the established research on Geosynthetic

durability it is possible to design a geotextile to fulfil its

function for the duration of the design life. However it is

imperative that the product selected uses an appropriate polymer

formulation, is manufactured from fibres produced to a controlled

specification and with fabric properties designed for long term

use. When selecting a geotextile a designer must take into

account not only the mechanical and hydraulic properties of the

geotextile at the point of manufacture, but the proven longevity

of the properties in the site environment, both prior to

installation and for the duration of the design. The consistency

of the material provided is imperative if the tests performed in

a laboratory are to be trusted. The use of geotextiles

manufactured from the bi-products of other manufacturing

processes must be undertaken with extreme caution as the long

term performance can never be fully known.

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References:

1. http://www.uaf.edu/files/ces/publications-db/catalog/cred/

CRD-00019.pdf

2. http://www.utexas.edu/research/ctr/pdf_reports/0_5812_1.pdf

3. Application Guide and Specifications for Geotextiles in

Roadway Applications by Jorge G. Zornberg and Nathan

Thompson

4.

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5. http://www.fibertex.com/SiteCollectionDocuments/Business

%20Areas/Geotextiles/031.371.01%20Introduktions

%20GB_2013feb_low.pdf

6. Federation of indian chambers of commerce and industry GeoTextiles : Perspective

from the Construction Sector

7. http://scholar.lib.vt.edu/theses/available/etd-03102006-

033808/unrestricted/SHY_ETD.pdf

8. http://www.geofabrics.com/docs/The%20durability%20of

%20geotextiles.pdf

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