With India’s rapidly developing economy and growing population there is enormous pressure to ensure large-scale infrastructure development. The resulting investment in roads, railways, power grid expansion, and water resources has the potential to create a huge market for geosynthetics.
Geosynthetics are manmade synthetic materials made of polymeric or natural materials in the form of a sheet, a strip or a three-dimensional structure. They are easy to produce and transport and can be used to make projects more environmentally sustainable. They perform five major functions – separation, reinforcement, filtration, drainage and containment.
Key geosynthetic products
Based on physical characteristics and manufacturing methods, geosynthetics can be classified into nine product categories – geotextiles, geomembranes, geogrids, geonets, geosynthetic clay liners, geofoam, geocells, geopipes and geocomposites.
- Geotextiles: Geotextiles are permeable textile materials made of polypropylene or polyester. They are not only the oldest but also the largest group of geosynthetics in terms of volume and are used in civil engineering for erosion control, soil stabilisation, reinforcement, separation and drainage. Geotextiles can be further divided into three categories – woven fabrics, non-woven fabrics and knitted fabrics. The Indian road sector is a major consumer of geotextiles. The government has been extensively deploying geotextiles for road projects in the Northeast which has high soil erosion. Besides, the Ministry of Textiles is incentivising the use of geotextiles by providing a subsidy to users. Apart from roads, geotextiles are an ideal material for many other infrastructure works such as pipelines, landfills, drainage structures, railways and various other civil projects. Non-woven geotextiles have been used in tunnel works of the Delhi metro and in the construction of tunnels in hilly regions. The use of geotextiles in highway, railway and port projects provides benefits of reduced maintenance costs and longer life cycle of the infrastructure asset.
- The Cabinet Committee on Economic Affairs has recently accorded approval for the setting up of the National Technical Textiles Mission with a total outlay of Rs 14.8 billion and a view to positioning the country as a global leader in technical textiles. The mission will have a four-year implementation period, from 2020-21 to 2023-24. It will also focus on the development of biodegradable technical textile materials, including geotextiles.
- Geogrids: Geogrids are polymeric products formed by joining intersecting ribs and have large open spaces called apertures. The direction of the ribs is referred to as the machine direction, which is oriented in the direction of the manufacturing process. The other direction is the cross machine direction, which is perpendicular to the machine direction ribs. Polymeric materials such as polyester, high density polyethylene and polypropylene form the main components of geogrids. Geogrids are commonly used to reinforce retaining walls, as well as sub-bases or subsoils below roads or other structures. Earlier, geogrids were only used for the construction of retaining walls. Later, geogrids also began to be used in many other structures such as pavements and dams due to their key properties of redistribution of load over a wider area, high tensile strength, high holding capacity and environment-friendly nature. They are also used to stabilise the subgrade for construction of embankments in the highway and railway sectors and also in the stabilisation of soils with low bearing strength or high water table levels where laying of foundations to carry heavy loads becomes critical. In the VisvesvarayaSetu project, the substructure was reinforced with bi-oriented geogrids using bottom ash as a filler material. Besides, the Northeast Frontier Railway has used geogrids in combination with geotextiles and sand layers for formation rehabilitation.
- Geomembranes: Geomembranes are thick impervious plastic sheets with a 0.5-3 mm thickness and are used primarily for linings and covers of liquid or solid storage facilities. Geomembranes are used to control fluid movement and are highly impermeable unlike geotextiles, geogrids and geocells. The lifespan and performance of the membranes depend upon the material used to manufacture them. Due to their ability to block fluids, they can help prevent the dispersal of contaminants and are therefore particularly important for waste management. Apart from this, geomembranes are being used in land/pond/canal/tunnel lining, and environmental, hydraulic, transportation, and oil and gas applications. However, geomembranes are relatively more expensive in unit terms as compared to other geosynthetic products.
- Geonets: They are usually formed by a continuous parallel set of polymeric ribs at acute angles to one another forming a net-like configuration. They are obtained by press forming of thermoplastic polymers or welding of threads/bands. Their design function is completely within the drainage area where they are used to convey fluids of all types. Geonets are especially used in landfills, foundation walls, methane roads and asphalt concrete pavements, and for erosion control and drainage. Despite mutual penetration of constructive layers, a geonet allows getting a jamming effect of structural fill material in meshes, which allows the control of horizontal slides. Due to its hardness properties, a geonet allows considerable loads to be sustained.
- Geosynthetic clay liners: Geosynthetic clay liners are rolls of factory-produced material mostly consisting of two layers of non-woven geotextiles with an intermediate layer of sodium bentonite powder. The two layers of geotextiles are joined together by a sewing process (needle-punched non-woven), thus creating a perfect stable mat with high internal shear resistance. On contact with water, the sodium bentonite in the mat swells up and creates a waterproof mineral layer. Geosynthetic clay liners are often used as hydraulic barriers for water, leachate or other liquids and even gases. They are also used as replacements for either compacted clay liners or geomembranes, or are used in a composite manner to augment the more traditional liner materials. Typical lining applications of geosynthetic clay liners include use in canals, storm water impoundments and wetlands, as landfill liners and landfill caps, for secondary containment and in highway and civil construction, and mines.
- Geofoams: Geofoams are blocks or slabs created by the expansion of polystyrene foam to form a low density network of closed, gas-filled cells. They are extremely light and can withstand harsh conditions. They are often used in fill applications where a lightweight material is required to reduce stresses on underlying soils or lateral pressures on retaining walls, abutments or foundations. Due to the advantages of low cost and better environmental sustainability, the demand for geofoams is expected to increase in the near future.
- Geocells: Geocells, or cellular confinement systems, are three-dimensional systems fabricated from ultrasonically welded high-density polyethylene strips that are expandable on site to form a honeycomb-like structure. They are filled with compact non-cohesive soils which are confined within the cellular walls and the composite forms a rigid to semi-rigid structure. Some of the key characteristics of geocells are chemical resistance, ageing resistance, high durability and inherent flexibility. They are widely used in construction for erosion control, soil stabilisation on flat ground and steep slopes, channel protection and structural reinforcement for load support and earth retention. Geocells have offered a viable solution for strengthening and fixing the water accumulation problem on State Highway-30 and the soil erosion problem in the widening of National Highway-91.
- Geopipes: They are perforated or solid-wall polymeric pipes used for drainage of liquids and gases. In some cases, the perforated pipe is wrapped with a geotextile filter. They are primarily used for leachate collection and in case of high compressive loads. Geopipes can also be used in landfill applications to facilitate collection and rapid drainage of the leachate to a sump and removal system.
- Geocomposites: Geocomposites are geosynthetics made from a combination of two or more geosynthetic types such as geotextile-geonet, geotextile-geogrid and geonet-geomembrane. These combinations provide benefits over individual layers of geosynthetics by enhancing functions, and increasing interface friction angles and the speed of installation. They are primarily used for separation, reinforcement, filtration, drainage and containment. On the basis of functionality, the geocomposites market is divided into three segments – drainage, containment and others. Of these, drainage is the leading segment, used in civil and road construction, trench drains, pavement base course or edge drains, tunnels in railways and roads, rooftops, retaining walls and bridge abutments, and other applications.
The use of geosynthetics has key advantages across infrastructure sectors. Comprising only a minor fraction of the total project cost, geosynthetics offer some of the most sought-after properties of durability and environment-friendliness. Besides, they prevent accidents, increase the life of structures and lead to the efficient use of natural resources. However, despite the benefits offered by geosynthetics and government initiatives for their promotion, particularly geotextiles, there is still a long way to go in ensuring extensive deployment of these materials in the infrastructure sector. The growing number of infrastructure projects though is expected to favour the growth of the geosynthetics market.