The increased use of geosynthetics is a much-needed step in a resource-constrained environment. Moreover, increasing infrastructure development has created a need for new techniques that are cost-and time-effective. These materials are used in almost all fields of civil engineering including transportation, the water sector, environment, and hydraulic systems.
Geosynthetics are a class of materials used in conjunction with soil to improve overall performance in a specific context. In general, they are planar products, manufactured from polymeric material used with soil, rock, earth or other geotechnical engineering-related material, such as fly ash, as an integral part of a project structure or system.
The use of geosynthetics reduces land requirement and ensures the preservation of the limited natural resources. Geosynthetics have been commonly accepted as durable, long lasting and environmentally safe solutions to geotechnical engineering projects. 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 post the use of geosynthetics. Its use also minimises the routine repair and maintenance costs of a structure.
Awareness about geosynthetic products has primarily risen post 2005 with international consultants incorporating these in their designs and the World Bank making geotextile use mandatory in infrastructure projects funded by it.
Geosynthetics are widely used in geotechnical applications such as civil engineering works (roads and pavements, slope stabilisation and embankment protection, tunnels, rail-track bed stabilisation, etc.), coastal engineering and environmental engineering. Some key players in the Indian geosynthetics market are Strata Geosystems, Techfab Geosynthetics, Terram India, GeosIndex and Enviro Geosynthetics Private Limited.
Geosynthetics are also extensively used in road and bridge projects. In addition, they are also widely used in railway, airport and seaport projects. Besides transport, segments like irrigation, solid waste management and soil erosion prevention in coastal areas and river-banks 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 material is incorporated within the soil to improve its engineering performance. Sheets of a geotextile/geogrid are embedded horizontally in soil structures. The stress developed in the soil mass is transferred to the geotextile sheets as tensile force through friction. The tensile strength of a geotextile/geogrid and its frictional resistance with the soil are primary features required for design. The use of this technology increases the service life of the structure and reduces maintenance costs.
The extensive use of geosynthetic material in civil engineering projects results in better quality control (as materials are manufactured in factories), rapid installation, cost competitiveness versus other construction material and lower carbon footprint, requirement of smaller parcels of land for the same engineering structures, etc.
Geosynthetics have made it possible to construct roads and pavements in difficult locations such as marshy stretches, those with soft/ organic deposits and in expansive soil areas. While geosynthetics can be used in the construction of the road itself, they can also be used in retaining soils of steep embankment slopes in areas where right of way is restricted and as reinforced soil walls for bridge approaches. These applications result in significant savings, improved performance and enhanced serviceability on a short-term and long-term basis.
Geosynthetics help in subgrade separation and stabilisation, base reinforcement, overlay stress absorption and reinforcement, etc. Drainage of water from pavements has always been an important consideration in road design. Geosynthetic materials help in the reduction of intrusion of stone aggregates into the soil subgrade. In the construction of areas with heavy traffic, such as parking lots, a stable subgrade with sufficient bearing capacity is required. When installed between the subsoil and the base course, geogrids are particularly well suited for this application.
Geosynthetic materials prevent reflective cracking in road pavements. Geotextiles or biaxial geogrids are generally used above the cracked surface before asphalt overlays are done. The durability of the overlay is prolonged due to the use of geosynthetic materials. The thickness of the overlay can also be reduced with the use of geosynthetic materials.
The huge pipeline of road projects in the country (especially with the launch of big-ticket programmes such as the Bharat Mala) 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. National highway projects executed in Visakhapatnam, Vallarpadam, Tuticorin and Paradip have used geosynthetics. Construction of the major district road (MDR) No. 82 near Daund and MDR No. 65 (Jejrui-Morgon) in Pune used woven geotextile for subgrade stabilisation. Development of the Gharni-Nitur-Nilanga section of State Highway 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.
The application of geosynthetics in the railway sector is similar to that in roads. Geosynthetics can be used in the construction of steep slopes (non-railways loading), embankment slip repairs, construction of high banks on soft soil, erosion control of slopes, and protection against rockfalls. Further, there are a number of applications specific to railway loading. These include track-bed design, reinforced earth embankments, and formation rehabilitation and high banks on soft soil, erosion control of slopes and protection against falling rocks. Erosion of railway embankments and hill slopes is caused principally by rain and wind. Erosion of the topsoil gradually destabilises earthen embankments. Geosynthetics can be an economical aid in improving train load carrying capability. These materials work as a separation barrier, prevent rutting and ballast puncturing, improve soil bearing capacity, and distribute load better.
In railway construction, geosynthetics can be installed within or beneath the ballast or sub-ballast layers, or both. 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. It has good hygroscopic and hydrophilic properties. When applied on an exposed soil surface, geo-jute acts like a miniature check dams or like a micro terrace. It reduces the kinetic energy of rain splashes, diminishes the intensity of surface run-off, prevents detachment and migration of soil particles, and ultimately helps in the quick growth of vegetation by the formation of mulch.
In 2014, Indian Railways announced that it was looking at using geosynthetics technology to improve the speed of trains on over 2,500 km of railway tracks, which have speed restrictions due to difficult terrain. Most of these corridors fall in the Konkan belt, and in the southern and eastern parts of the country.
Geosynthetics are used in airport construction for creating space for runways and reinforcing pavements. Steep reinforced embankments or gabion walls provide the flat area for runways and other infrastructure.
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.
Other key sectors
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 function as protection, separation and drainage for the top concrete lining.
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 geo-containers 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.
So far, the penetration of geosynthetics has been fairly low across the country. However, geosynthetics have now become integral to almost all road projects in India and are being used in pavements, embankments, approach roads for bridges, runways for airports, approach roads for seaports, etc. Some of the key inhibiting factors include low industry-wide acceptance, non-uniform standards and procedures, diffidence in application of the new technology, lack of confidence in designers and lack of coordination between the textiles and geotechnical engineering industries. Going forward, massive infrastructure expansion plans, especially in the highway and railway sectors, are expected to drive the demand for geosynthetics in India.