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GEO TEXTILES

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ABSTRACT:

Geotextiles have been used very successfully in road construction for over 30

years. Their primary function is to separate the sub base from the subgrade resulting in a

stronger road construction. The geotextile performs this function by providing a dense

mass of fibers at the interface of the two layers. It is suggested that the ability of a

geotextile to act as a separator is largely independent of the mechanical characteristic of

the geotextile and that strain softening geotextiles can still perform this role when

strained past their peak values. A strain energy approach to design is not routine in

geotechnical engineering design, as it is difficult to quantify the external energy supplied

to the system and the internal energies of the individual components making up the

construction. Recent research has suggested that an equivalence of strain energy, between

different geotextile types, may exist up to the in service strain. Comparing the actual

strain energy and that calculated using a simplified approach shows that significant errors

are introduced by firstly ignoring the nonlinear characteristics of the stress-strain curve

and secondly by not considering the entire area under the stress-strain curve to rupture of

the geotextile. Based on the difficultly in using the strain energy approach in geotechnical

engineering design and the significant inconsistencies that can exist in its calculation, it is

suggested that the concept of strain energy is not an appropriate parameter for

characterising geotextiles.

INTRODUCTION:

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Geotextiles have proven to be among the most versatile and cost-effective ground

modification materials. Their use has expanded rapidly into nearly all areas of civil,

geotechnical, environmental, coastal, and hydraulic engineering. They form the major

component of the field of geosynthetics, the others being geogrids, geomembranes and

geocomposites. The ASTM defines geotextiles as permeable textile materials used in

contact with soil, rock, earth or any other geotechnical related material as an integral part

of civil engineering project, structure, or system. Based on their structure and the

manufacturing technique, geotextiles may be broadly classified into woven and

nonwoven. Woven geotextiles are manufactured by the interlacement of warp and weft

yarns, which may be of spun, multifilament, fibrillated or of slit film. Nonwoven

geotextiles are manufactured through a process of mechanical interlocking or thermal

bonding of fibers/filaments.

Mechanical interlocking of the fibers/filaments is achieved through a process

called needle punching. Needle-punched nonwoven geotextiles are best suited for a

wide variety of civil engineering applications and are the most widely used type of

geotextile in the world. Interlocking of the fibers/filaments could also be achieved

through thermal bonding. Heat-bonded geotextiles should be used with caution, as they

are not suitable for filtration applications or road stabilization applications over soft soils.

RAW MATERIAL OF GEOTEXTILE:

The four main polymer families most widely used as the raw material for geotextiles are:

1. Polyester

2. Polyamide

3. Polypropylene

4. Polyethylene

The oldest of these is polyethylene, which was discovered in 1931 in the research

laboratories of the ICI. Another group of polymers with a long production history is the

polyamide family, the first of which was discovered in 1935.The next oldest of the four

main polymer families relevant to geotextile manufacture is polyester which was first

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announced in 1941.The most recent polymer family relevant to geotextiles to be

developed was polypropylene, which was discovered in 1954. The comparative

properties of these four polymer are shown in very general items in Table

Polyester Polyamide Polypropylene Polyethylene

Strength H M L L

Elastic modulus H M L L

Strain at failure M M H H

Creep L M H H

Unit weight H M L L

Cost H M L L

Resistance to:

U.V. light

stabilized

H M H H

unstabilized H M M L

Alkalis L H H H

Fungus, vermin M M M H

Fuel M M L L

Detergents H H H H

H: High; M: Medium; L: Low

THE BASIC PROPERTIES OF GEOTEXTILE:

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The properties of polymer material are affected by its average molecular weight (MW )

and its statistical distribution. Increasing the average MW results in increasing:

tensile strength

elongation

impact strength

stress crack resistance

heat resistance

TYPES OF GEO TEXTILES:

woven geo-textiles

Non-woven geo-textiles

Knitted geo-textiles

Geo Textiles are the largest group of geo synthetics in terms of volume and are used

in geo technical engineering, heavy construction, building and pavement construction,

hydrogeology, environment engineering.

WOVEN GEO-TEXTILES

A fabric or synthetic material placed between the soil and a pipe, gabion or

retaining wall; to enhance water movement and retard soil movement and act as a blanket

to add reinforcement and separation. Coastal works, water ways, embankments and in

forming. Geocell for road

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Woven geo-textiles on concrete basis

NON-WOVEN GEO-TEXTILES

Filtration, drainage, reinforcement between soil stone or aggregate and in roads,

railways works, erosion prevention and separation. As filter fabric for dams, under

drainage system liners for pile foundation, coated PVC and bitumens to skin traction.

Non-woven geo-textiles in filtration

KNITTED GEO-TEXTILES

Knitted bags for protection of dams riverbank etc. Warp knitted fabric of

Kevlar yarns used in automobile and marine application. It is also used with foundations,

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soil, rock, earth or any other related material as an integral part of human man made

project, structure or system.

Reinforcement knitted geo-textiles

reinforcement and separation

reinforcement and anti-contaminating

reinforcement and filtration

FUNCTIONS OF GEOTEXTILE:

The mode of operation of a geotextile in any application is defined by six discrete

functions:

Separation

Filtration

Drainage

Reinforcement

Sealing

Protection.

Depending on the application the geotextile performs one or more of these functions

simultaneously. The protection function is not discussed here as it is not related to

transportation applications.

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SEPARATION:

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

geotextiles role in preventing the intermixing of two adjacent soils.

Geotextile installed as separation beneath roadbed.

For example, by separating fine subgrade soil from the aggregates of the base course, thegeotextile preserves the drainage and the strength characteristics of the aggregate

material.

FILTRATION:

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 filters 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.

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Edge Drain wrapped with Geotextile

REINFORCEMENT

In this method, the structural stability of the soil is greatly improved by the tensilestrength of the geosynthetic material. This concept is similar to that of reinforcing

concrete with steel. Since concrete is weak in tension, reinforcing steel is used to

strengthen it. Geosynthetic materials function in a similar manner as the reinforcing steel

by providing tensile strength that helps to hold the soil in place. Reinforcement provided

by geotextiles or geogrids allows embankments and roads to be built over very weak soils

and allows for steeper embankments to be built.

Soil Reinforcement of an Embankment using a Geosynthetic.

DRAINAGE

Although filtering applications are commonly referred to as drainage applications, they

are different. Drainage applications refer to situations where the water flows within the

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plane of the geosynthetic product (in-plane drainage). In filtration applications, the water

flows across the plane of the material.

Although certain types of geotextiles provide some in-plane drainage, most drainage

situations require a geo-composite drainage product such as prefabricated sheet drains

that provide a much greater drainage capacity.

Diagram showing the basic layout of a vertical sand filter with drainage

The filter bed should consist of the following elements:

20cm of top soil

Layer of geotextile

Drainage pipes bedded in the upper half of a 20cm layer of 10/40 aggregate (non

calcaire - limestone)

70cm layer of sand

Another layer of geotextile

Drainage pipes bedded in the lower half of a 20cm layer of 10/40 aggregate (non

calcaire - limestone)

All surrounded by a non permeable film.

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SEALINGS

A nonwoven geotextile performs this function when impregnated with asphalt or

other polymeric mixes rendering it relatively impermeable to both cross-plane and in-

plane flow. The classic application of a geotextile as a liquid barrier is paved road

rehabilitation. Here the nonwoven geotextile is placed on the existing pavement surface

following the application of an asphalt tack coat. The geotextile absorbs asphalt to

become a aterproofing membrane minimizing vertical flow of water into the pavement

structure.

HDPE- High Density Polyethylene Liners

HDPE is the most widely used geomembrane today. It has been the choice of many for

large critical containment applications.

Resistant to a wide range of chemicals on account of density >.94/cm3

Reliable in exposed environment due to high UV protection against degrading and

low temperature brittleness

PROTECTION

stream bed is the channel bottom of a stream,riveror creek; the physical confine of thenormal water flow. The lateral confines or channel margins, during all but flood stage, are

known as the stream banks or river banks. In fact, a flood occurs when a stream

overflows its banks and flows onto its flood plain. As a general rule, the bed is that part

of the channel, just at the "normal" water line and the banks are that part above the water

line.

http://en.wikipedia.org/wiki/Streamhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Flood_stagehttp://en.wikipedia.org/wiki/Floodhttp://en.wikipedia.org/wiki/Flood_plainhttp://en.wikipedia.org/wiki/Channel_(geography)http://en.wikipedia.org/wiki/Streamhttp://en.wikipedia.org/wiki/Riverhttp://en.wikipedia.org/wiki/Flood_stagehttp://en.wikipedia.org/wiki/Floodhttp://en.wikipedia.org/wiki/Flood_plainhttp://en.wikipedia.org/wiki/Channel_(geography)

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However, because water flow varies, this differentiation is subject to local

interpretation. Usually, the bed is kept clear of terrestrial vegetation, whereas the banks

are subjected to water flow only during unusual or perhaps infrequent high water stages

and therefore, might support vegetation some or much of the time.

GEOTEXTILE REQUIREMENT:

Selecting a geotextile for paved road depends upon the geotextile survivability. If

a roadway system is designed correctly, then the stress at the top of the subgrade due to

the weight of the aggregate and the traffic load is less than the bearing capacity of the

subgrade plus a safety factor. However the stresses applied to the subgrade and the

geotextile during the construction is much greater than that applied during service.

Therefore, selection of the geotextile in roadway applications is usually governed by the

anticipated construction stresses. The geotextile must survive the construction operations

if it is to perform the intended function of separation and filtration.

These survivability requirements are based on properties of geotextiles, which

have performed satisfactorily. Judgment and experience our required to select final

specification values. For large projects geotextile survivability should be verified by

conducting field tests under sitespecific conditions. The selected geotextile must also

retain underlying soil fines, while allowing a relatively unimpeded flow of water. Hence

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the geotextile Opening size and Permeability should be ascertained to match the site

requirements.

CONCLUSION:

Geotextiles are effective tools in the hands of the civil engineer that have proved

to solve a myriad of geotechnical problems. With the availability of variety of products

with differing characteristics, the design engineer needs to be aware of not only the

application possibilities but also more specifically the reason why he is using the

geotextile and the governing geotextile functional properties to satisfy these functions.

Design and selection of geotextiles based on sound engineering principles will serve the

long-term interest of both the user and the industry.

REFERENCES:

1. Robert M. Koerner Designing with Geosynthetics, 1998

2. http://www.drexel.edu/gri/gmat.html

3. John N.W. M Geotextile , 1987

4. TANFEL Advertisement report 1990

5. http://www.geofabrics.com.au/bidim.htm#filtration

6. http://www.geofabrics.com.au/bidim.htm#embankment

7. http://www.ag.ohio-state.edu/~ohioline/aex-fact/0304.html

8. http://www.acf-environ.com/stabprod.html

9. http://www.cofra.com/typar.html

10. www.multigeo.com

11. www.jute-industry.com/jute-textiles/geo-textiles.html

12.N. W. M. John - Technology & Engineering 1987 Geotextiles

http://www.drexel.edu/gri/gmat.htmlhttp://www.geofabrics.com.au/bidim.htmhttp://www.geofabrics.com.au/bidim.htmhttp://www.ag.ohio-state.edu/~ohioline/aex-fact/0304.htmlhttp://www.acf-environ.com/stabprod.htmlhttp://www.cofra.com/typar.htmlhttp://www.multigeo.com/http://books.google.co.in/books?q=+inauthor:%22N.+W.+M.+John%22http://books.google.co.in/books?q=+subject:%22Technology+%26+Engineering%22http://books.google.co.in/books?id=oZEOAAAAQAAJ&pg=PP1&dq=geotextiles&cd=1http://www.drexel.edu/gri/gmat.htmlhttp://www.geofabrics.com.au/bidim.htmhttp://www.geofabrics.com.au/bidim.htmhttp://www.ag.ohio-state.edu/~ohioline/aex-fact/0304.htmlhttp://www.acf-environ.com/stabprod.htmlhttp://www.cofra.com/typar.htmlhttp://www.multigeo.com/http://books.google.co.in/books?q=+inauthor:%22N.+W.+M.+John%22http://books.google.co.in/books?q=+subject:%22Technology+%26+Engineering%22http://books.google.co.in/books?id=oZEOAAAAQAAJ&pg=PP1&dq=geotextiles&cd=1