Geosynthetics are a family of polymeric products used to solve civil engineering problems encountered in infrastructure development, and are especially used to stabilise the terrain. Their use has expanded rapidly into nearly all areas of civil, geotechnical, environmental, coastal and hydraulic construction. In the infrastructure domain, geosynthetics are widely used to construct retaining walls and steep slopes, highways, airports and municipal landfill sites for ground improvement and shore protection works, etc.
The use of geosynthetics reduces the land requirement for projects and ensures the preservation of the limited natural resources. These materials have been commonly accepted as durable, long-lasting and environmentally safe solutions to geotechnical engineering projects. While the cost of geosynthetics is usually between 3 and 5 per cent of the total project cost, a number of projects have reported cost savings of up to 30 per cent with the use of geosynthetics. Its use also minimises the routine repair and maintenance costs of a structure.
Geosynthetics are extensively used in road and bridge projects. In addition, they are also widely used in railway, airport and seaport projects. As per industry experts, the road sector constitutes a majority share in the use of geosynthetics, at about 40 per cent. Besides transport, segments like irrigation, solid waste management and soil erosion prevention in coastal areas and riverbanks also offer large opportunities for geosynthetic use. Geosynthetic products are being used in riverbank revetment protection, coastal revetment protection, canal and water channel protection, etc.
The huge pipeline of road projects in the country (especially with the launch of big-ticket programmes such as Bharatmala) will provide a significant market for geosynthetics. According to the Confederation of Indian Industry, even a 5 per cent penetration of geosynthetics in road infrastructure development will create a market of Rs 50 billion per year. For accelerating the use of geosynthetics in road construction, the Ministry of Textiles is incentivising its usage by providing a subsidy.
National highway projects executed in Visakhapatnam, Vallarpadam, Tuticorin and Paradip have used geosynthetics. The construction of the major district road (MDR) No. 82 near Daund and MDR No. 65 (Jejrui- Morgon) in Pune used woven geotextiles for subgrade stabilisation. The development of the Gharni-Nitur-Nilanga section of State Highway (SH)-167 and the Taluka-Nilanga section in Maharashtra also used geosynthetics for subgrade stabilisation. A number of rural road projects being implemented under the Pradhan Mantri Gram Sadak Yojana have also used geosynthetic material for construction.
In railway construction, geosynthetics can be installed within or beneath the ballast or sub-ballast layers, or both. The geosynthetics commonly used in this application are geotextiles, geogrids, geocomposites and geocells. A railway track is one of the few applications which utilises all four types of geosynthetics. Geo-jute, along with a blanket layer for drainage purposes, is among the commonly used geosynthetics in railways. Jute geotextile or geo-jute is biodegradable and environment-friendly.
Geosynthetics can be used in the construction of steep slopes (non-railway loading), embankment slip repairs, construction of high banks on soft soil, erosion control of slopes, and protection against rockfalls. Further, there are several applications specific to railway loading. These include track-bed design, reinforced earth embankments, formation rehabilitation and high banks on soft soil, erosion control of slopes and protection against falling rocks.
Geosynthetics are used in airport construction for runways and reinforcing pavements. Steep reinforced embankments or gabion walls provide the flat area for runways and other infrastructure.
The development of Pakyong airport in Sikkim involved the use of geosynthetics. The runway was constructed by utilising huge amounts of earth cut from a hill to fill the valley side and get a level platform. A composite soil reinforcement system has been used to retain and stabilise this fill, the height of which varies from 30 metres to 74 metres. This flexible, draining type of retaining structure is said to be the tallest reinforced soil structure in the world.
Port development and dredging activity also use geosynthetics. Geotextiles are placed under rock ripraps or precast concrete blocks to prevent coastal erosion. They are also used as silt fences at construction sites to arrest soil particles from the run-off water. Geotextile tubes are used in dredging activities, while geocontainers are used for the disposal of potentially hazardous dredged materials offshore. For this, geotextile sheets are laid at the bottom of dump barges filled with dredged sediments and sewn. The containers are then transported to the disposal site and dumped using split hull barges.
Geosynthetics are also used for tunnel construction work in urban rail projects like the Delhi metro. They are a standard feature in metro track construction and make it possible to use faster and more effective construction methods, thus saving time and money in comparison to traditional construction methods. The Delhi metro project routinely uses non-woven geotextiles for its tunnelling sections. These geotextiles serve a protection, separation and drainage function for the top concrete lining.
The massive project line-up in the infrastructure space is a major positive for the geosynthetics industry. Sectors such as irrigation, railways, roads and tunnels are expected to offer significant opportunities in the coming years. As a policy initiative, the use of geosynthetics should be made mandatory where environmental and social benefits could be realised even while there is no overall economic benefit. It would also help in taking up trial projects as was done in the US and Europe in the early days of geosynthetics deployment. Most importantly, engineers need to be made aware of the geosynthetics technology by way of short courses or regular courses in universities. This will go a long way in increasing the use of geosynthetics in infrastructure projects.