Geotextiles are porous fabrics manufactured from synthetic materials such as polypropylene, polyester, polyethylene, nylon, polyvinyl chloride and various mixtures thereof.

They are available in roll lengths of up to 2000 feet, in widths from 10 to 300 miles (1 mile = 1/1000 inch) up to 30 feet in width. The permeability of geotextile sheets is comparable to that of coarse gravel to fine sand. They are either woven from continuous monofilament fibers or non-wovens made using thermal or chemical bonding of continuous fibers and pressed by means of rollers into relatively thin fabrics. These fabrics are sufficiently strong and durable even in adverse soil environment. They have a pH resistance of 3 to 11.

The use of geotextiles in geotechnical engineering has been increasing in popularity over the past several years. Geotextiles can be used in many ways. They are used as soil separators, used in filtration and drainage, used as reinforcement material to increase the stability of earth mass, used for control of erosion, Etcetera. Some of the uses of geotextiles are described in the following sections.

geotextile as separator

Figure-1 Geotextiles as Filter Media
Figure-1 Geotextiles as Filter Media

A properly graded filter prevents erosion of the soil in contact with it due to leakage forces. To prevent erodible soil from passing into or through the filter, the pore space between the filter particles must be small enough to hold some of the protected material in place. If the filter material is not designed properly, small particles from the protected area can move into the pores of the filter material and prevent proper drainage.

As an alternative, geotextiles can be used as a filter material in place of filter soil as shown for an earth dam. Figure 1, Other uses of geotextiles as separators are:

1) Separation of natural soil subgrades from stone aggregates used as pavements of roads etc.

2) As a water proofing agent to prevent cracking in existing asphalt pavement.

geotextiles as reinforcement

Fig-2 Use of geotextiles in pavement
Fig-2 Use of geotextiles in pavement

Geotextiles with good tensile strength can contribute to the load bearing capacity of soils that are poor in tension and good in compression.

Geotextiles placed between the natural subgrade below and the stone aggregate above in unpaved roads not only act as separators but also increase the bearing capacity of the subgrade to take heavy traffic loads. Here, the geotextile acts as the reinforcer as shown in line drawing number 2,

Another major way in which geotextiles can be used as reinforcement is in the construction of fabric-reinforced retaining walls and embankments. This technique is borrowed from the technology for reinforced earth walls. Geotextiles have been used to create walls that can simultaneously provide both a facing element and stability.

Fig-3 Geotextiles in retaining walls
Fig-3 Geotextiles in retaining walls

Shown in the process of building a wall with granular backfill Fig-3, The procedure is as follows.

1) Level the work surface.

2) Lay the geotextile sheet 1 of appropriate width on the surface with 1.5 to 2 meters on the surface by wrapping it as temporary wood on the wall face as shown Fig-3(a),

3) Backfill this sheet with granular soil and compact it using a roller of suitable weight.

4) After compaction, fold the geotextile sheet as shown in Fig-3(b),

5) Lay out the second sheet and continue the process as before. shown in full wall Fig-3(d)

The front of the wall can be secured using shotcrete or gunite. Shotcrete is a mixture of sand and cement with a low water content, often with additives, that is sprayed onto a surface at high pressure, similar to ganite. The design of geotextile reinforced walls is similar in principle to reinforced earth walls.

Geotextiles in Filtration and Drainage

Geotextile sheet has been used successfully to control the erosion of land surface. Erosion of exposed surfaces can occur due to rain water falling or running water in rivers etc. Fig-4(b) Shows a schematic diagram for protecting the banks of running water.

Figure-4 Use of Geotextiles for Erosion Control
Figure-4 Use of Geotextiles for Erosion Control

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.