Application of geotextiles in railroads

Geotextiles are permeable textile structures made of polymeric materials and are used mainly in the civil engineering applications in conjunction with soil, rock and water, says Dr Nemailal Tarafder.

Geo-textiles are members of a large family called geo-synthetics. Geo-synthetics may perform the following functions in new track construction rehabilitation: separation of materials with different particles size distributions, filtration, drainage, and soil reinforcement. In railroad construction, geo-synthetics may be installed within beneath the ballast or sub-ballast layers. Emphasis will be given to the use of geo-synthetics within and beneath ballast and/or sub-ballast layers.

Geo-synthetics that are commonly used in this application are geo-textiles, geo-grids, geo-composites and geo-cells. Geo-textiles are permeable textile structures made of polymeric materials and are used mainly in the civil engineering applications in conjunction with soil, rock and water. In the first modern use, commercial geo-textiles, which are also known as filter fabrics were used for erosion control. The first geo-textiles were woven from mono-filaments in 1950, with a high percentage of open area. Non-woven needle punched fabrics were introduced in Europe in 1960. The first non-woven (thermal bonded needle punched) geo-textiles were introduced in the US in 1972.

The problem of tracks getting washed away because of rain, brimming natural basins, floods and coastal disturbances may be a thing of the past if the railways´ new experimentation of using jute to hold soil together succeeds. The Eastern Railways has undertaken a exercise to give a boost to the sagging of jute industry. Recently, rehabilitation work on tracks at two sections under Howrah Division using jute geo-textile technique, which is considered a superior method, to the one currently in use has, been taken up. The areas are on the 6.61 km Baltikuri-Dankuni section and the 4.67 km Balighat-Dankuni section under Howrah Division in West Bengal.

The Railways intend to use geo-textiles not only as a blanketing layer on the formation of the tracks, but along under slopes of the formation for arresting erosion of soil. This will do away with the practice of using steel and iron nets to hold boulders stacked for strengthening the embankment. According to officials, tests have yielded encouraging results in controlling subsidence of pavement, arresting migrating of soil particles, serving as a drainage layer along its plane, prevents puncturing of formation by the ballast. Moreover, it is cheap and organic.

These are used in geo-technical engineering, heavy construction, building and pavement construction hydrology and environmental engineering. Geo-textiles are designed for one or more of the following functions:-

(a) separation (b) filtration (c) protection (d) drainage and (e) reinforcement When integrated with polymeric sealing materials, geo-textiles acts as a moisture barrier as well.

Geotextile materials and manufacturing techniques
Geo-textiles are traditional textile products such as woven and non-woven fabrics. The most important factors in manufacturing of geo-textiles are polymeric type, fibre type, fabric design and type of bonding (for non-woven). Common types of geo-textiles are plain, satin and twill. Non-woven manufacturing of geo-textiles includes fibre production, fibre preparation, web bonding and finishing. Filaments or short fibres are first arranged into a loose web, then bonded together by a chemical, thermal or mechanical bonding process. In a chemical bonding process, which is used the best, a cementing medium such as glue, latex or resin is added to bind the filaments or short fibres together. The impregnated web is then calendared.

In the thermal bonding process (also called heat bonding), filaments or s