GeoTextiles.pdf

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Engineering Use of Textiles in Geotextile

By: Tripti Basant* & Shahnaz Jahan**

*Research Scholar, **Professor and Head Department of Clothing & Textiles, Govind Ballabh Pant University of Agriculture & Tethnology,

Pantnagar

Geotextiles used in civil engineering applications are expected to carry out one or more functions over if given design life. There are five defined functions, these are; drainage, separation, filtration, protection and reinforcement. Geotextiles are normally manufactured by either woven or non-woven techniques. The functional requirements of the geotextile in a given application will determine the performance properties required, and any assessment of the products durability will be based on the degradation of these properties over a given time.

Geotextiles particularly refers to permeable fabric or synthetic material, woven or non-woven, which can be used with geotechnical engineering material. They apply to a broad range of civil engineering construction, paving, drainage and other applications. Geotextiles are extensively used with soil, rock, earth or any other geotechnical engineering-related material.

HISTORY OF GEOTEXTILES

Prior to 1988, geotextiles were called plastic filler cloth or filter fabric. Because of the increase in the number of products being manufactured to be used as filter cloth, the specifications were revised. This material is now identified as Geotextile.

The term geotextile was first proposed by Giroud and Perfetti in 1977. A Geotextile is a semi permeable rot-proof geosynthetic comprised solely of textiles. The ASAE defines a geotextile as a fabric or synthetic material placed between the soil and a pipe, gabion, or retaining wall to enhance water movement and retard soil movement.

GEO-TEXTILE FORMING FIBRES AND POLYMERS

Natural forms of Geotextiles: Jute, Flax, Coconut (Coir), Cotton and Hemp, etc.

Composite/Synthetic materials for geotextiles

Geo fibres are usually polypropylene fibers blended into soils to create an ideal reinforcement system for the repair of slope failures, reinforcement of pavement and foundation stabilization.

ESSENTIAL PROPERTIES OF GEOTEXTILES

1. Mechanical Properties Mechanical properties include the ability of a textile to perform work in stressed environment strength and elongations are main mechanical properties of geo textiles.


2. Filtration ability The filtration effect is achieved by placing the textile against the soil, in close contact.

3. Chemical resistance There are mainly four agents of deterioration of geotextile-organic (microorganisms), inorganic (pH), light exposure and time. But inclusion of additives, in the form of antioxidants and carbon black powder can considerably reduce this effect.

APPLICATION AREAS OF GEO TEXTILES

Roadways, parking lots, loading areas and construction sites

Prevent drainage systems from clogging with fine particles

Prevention of weed growth (in horticulture applications)

Moisture conservation (in horticulture applications)

Fluid transmission

For waterway erosion control

Filtration, Protection and separation function

Erosion control

Geogrids installed on steep slopes prevent in washing soil particles from surface. Geo-textiles allow the water to pass through but resist the fine soil migration. After vegetation, which provides erosion control of slope, becomes grown, the geogrid will decompose after several years.

Separation

Geo textiles can be used as separator between subsoil and aggregate layer of roads. This protects the aggregate layer from sinking in the subsoil. At the same time it is permeable to water.

Filtration

The filtration function of a geotextile serves the same purpose as the separation function, but under different circumstances. Geo textile has become a solution for draining out the accumulated water from areas like coal yards. It is filter media to retain soil particles of backfill material in place, while it allows the release of accumulated hydraulic pressure.

Protection

Soil waste and hazardous landfill structures are designated with impervious geo-membrane layer along with geo textile thus ensuring that no ground water contamination takes place. It also acts as drainage gallery. It is used in the thermal power stations for disposing off the fly ashes in the ash-ponds constructed with impervious geo-membrane layer along with geo textile that protects the membrane from punching and soil polluting.


Drainage

Drainage function is defined as The collecting and transporting of ground water and/or other fluids in the plane of the geotextile. It is the ability of the geotextile to drain fluids on its own, meaning that it is not part of a drainage system, but is the drainage system itself.

When a geotextile forms part of a drainage system, where the geotextile is used to separate a soil and a coarse-grained drainage layer, the function is filtration.

Paving

Geotextile provides several benefits to pavements. It acts as a stress relieving interlayer. It retards the reflection cracks, reduces road maintenance costs, increases the road life and improves the pavement service ability.

Reinforcement

Soils have relatively low tensile strength so that they are not able to transfer all of forces arising in a structure when it is loaded. The tensile forces created can be transferred using geosynthetics products used as a reinforcing element, hence the term reinforced soil. Geosynthetics materials will form a base composite by grainy material interlocking which is effective even on the substrates formed by peat or soft silt.

Benefits of use of geosynthetics materials for reinforcement:

Improvement the mechanical properties of soils

Unsuitable types of soils can be used

Expensive structural designs are avoided

Undesirable mixing of soils and demands for earth moving are minimized

Minimum land required

Natural noise reduction barriers/walls are easily constructed

Natural appearance of landscape is maintained

Table 1: Fabric Types of Geo-textiles

Fabric Type Application Area

Woven geo-textiles Coastal works, water ways, embankments

Non woven geo-textiles

Filtration, drainage, erosion prevention, separation and soil reinforcement in roads, railways work

Knitted geo-textiles Knitted bags for protection of dams riverbanks etc.

TYPES OF GEO-TEXTILES MATERIALS

Geo-membranes

Geomembranes are impermeable liquid or vapour barriers made from continuous polymeric sheets. They act as a liquid or vapour barriers due to extremely low permeability. They are also used as buffers against pollutants.


Geomembranes are made from impregnation of geotextiles with asphalt or elastomer sprays. They are not absolutely impermeable but are relatively impermeable when compared to geotextiles or soils or even clay soils. Nowadays they are increasingly being used in reservoirs, ponds, lined canals and other geotechnical projects.

Geogrid

It is a thick plastic mesh, which provides a strong path foundation. It spreads the weight of path use over the full path length and width. Grid structure prevents path material from moving along, or across the matting and migrating from the path sides into the peat.

Matting

Mattings of natural materials used to cover the soil surface to reduce erosion from rainfall impact, hold soil in place, and absorb and hold moisture near the soils until vegetation is established. Mattings are commonly applied on short, steep slopes where erosion hazard is high and vegetation will be slow to establish. They are also used on stream banks where moving water at velocities between 3 ft/s and 6ft/s are likely to wash out new vegetation and in areas where the soil surface is disturbed and where existing vegetation has been removed.

Geo cell

Geo cell is available in a polymer cellular form including a regular open network of connected strips, linked by extrusion, adhesion or by other methods.

Geo composite

A geo-composite comprises with a mixture of:

Geotextile and geogrid

Geogrid and geomembrane

Geo-textile and any of these three materials with another material

CONCLUSION

The majority of applications that call for the use 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 required properties for the duration of the design. It is possible to design a geotextile to fulfill 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 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.

This article was originally published in the Textile Review magazine, November, 2012, published by Saket Projects Limited, Ahmedabad.

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