Geosynthetics are man-made polymers that are used to improve soil quality and achieve better performance in geotechnical engineering projects. They are easy to produce and transport and can be used to create more environmentally sustainable projects. They perform five major functions – separation, reinforcement, filtration, drainage and containment.
Types of geosynthetic products
Geosynthetics are available in a wide range of forms and materials. They can be broadly classified into nine categories based on their physical characteristics and method of manufacturing – geotextiles, geomembranes, geogrids, geonets, geosynthetic clay liners, geofoam, geocells, geopipes and geocomposites. Among these, geotextiles have the largest share in production, followed by geomembranes and geogrids.
- Geotextiles: They are permeable fabrics manufactured from synthetic materials such as polypropylene or polyester which when used in association with soil, help in controlling erosion and maintaining stability. They are not only the oldest but also the largest group of geosynthetics in terms of volume. Geotextiles usually come under three different categories:
- Woven fabrics: As the name suggests, woven fabrics are manufactured by adopting techniques that are similar to weaving of usual clothing textiles. They are made by interlacing two sets of threads or yarns. These fabrics take longer to make but have high tensile strength and load capacity. They are generally preferred in applications where high strength properties are needed and filtration requirements are less critical.
- Non-woven fabrics: Non-woven fabrics, which have a felt-like texture, are often quicker and cheaper to create but have shorter lifespans. The main functions of these products are filtration and separation. The characteristics of these fabrics depend upon the type of raw material, structure of the fibre matrix and bonding method. The fibres can be bonded together by adopting thermal, chemical or mechanical (needle punching) techniques.
- Knitted fabrics: Knitted geotextiles are formed using the knitting technique. The process consists of interconnecting loops of yarn on powered automated machines. They are mainly used for soil reinforcement and embankment support functions.
- Geotextiles are an ideal material for many infrastructure works such as roads, pipelines, landfills, drainage structures, railways and various other civil projects. Depending on the function, they are used in an open-mesh version (woven), warp-knitted structure or with a closed-fabric surface (non-woven). They have proven to be among the most versatile and cost-effective ground modification materials.
- Geotextiles are increasingly being used to control soil erosion on hillsides and embankments because the country faces a high level of soil loss each year during the monsoon season. The Rajiv Gandhi Setu in Daman, for example, used high strength polyester woven geotextiles from Techfab India Industries to reinforce the embankment and provide a separation layer. Another instance is the Karnataka State Highway Improvement Project where a substantial quantity of non-woven geotextiles was used to improve the road network.
- Increasing population, rapid urbanisation and increasing investments in infrastructural developments are some of the major factors that will drive the growth of geotextiles in the country. Upcoming road and railway networks including high speed train projects will emerge as significant application areas for geotextiles. Non-woven fabrics have dominated the geotextiles market in India and the segment will continue to lead the market in coming years as well.
- Geomembranes: They are continuous, thick plastic sheets manufactured from one or more synthetic materials. They are impermeable membranes used with rocks or earth to block gas or fluid migration in man-made structures. They are usually made of synthetic polymers in sheets with a thickness of 0.25-3.5 mm. 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, therefore, they are particularly important for waste management. The market for geomembranes is driven by their increasing use in waste management applications and in various industries against land and water contamination (as a result of strict environment protection regulations). Geomembranes are also used for waterproofing of dams and canals. Projects where geomembranes have been used for waterproofing include the Kadamparai dam in Tamil Nadu and the Tanakpur canal in Uttarakhand.
- Geogrids: They are geosynthetic materials which are formed by joining intersecting ribs. Polymeric materials such as polyester, high density polyethylene and polypropylene form the main components of geogrids. They have large open spaces in between the ribs known as apertures. The direction of the ribs can be of two kinds – one in the machine direction (md), conducted in the direction of the manufacturing process and the other, cross-machine direction (cmd), perpendicular to the machine direction ribs. They can be manufactured using three methods – extrusion, weaving and knitting. They are used in the construction industry as reinforcing materials as they have high tenacity and ability to distribute load across a larger area. They are used to stabilise the subgrade for construction of embankments, highways and railway tracks and also for stabilisation of soil with low bearing strength. The project involving the improvement of the Tasgaon-Kavathe Mahankal road used geogrids for subgrade stabilisation and the basal reinforcement of existing road stretches that got heavily waterlogged during the monsoon.
- Geonets: They are formed by two sets of coarse, parallel, extruded polymeric strands intersecting at a constant acute angle. The network forms a sheet with in-plane porosity that is used to carry relatively large fluid or gas flows. They are used almost exclusively for their drainage capability. The major applications of geonets are in landfills, foundation walls, methane roads, asphalt concrete pavements, erosion control and drainage.
- Geosynthetic clay liner: It is a fabric-like material which acts a hydraulic barrier and consists of two layers of textiles joined with bentonite clay. They are often stitched or needle punched through the bentonite core to increase internal sheer resistance. The sodium bentonite layer exhibits various beneficial properties such as low permeability and, thus, acts as a natural sealant. The materials also exhibit long-lasting resistance against harsh physical and chemical conditions, making them a preferred choice for composite landfill materials. They find applications in lining systems of construction, mining, upstream oil and gas exploration sites, etc. They are also the preferred lining material in canals and wetlands. Growing awareness regarding safe disposal and waste water treatment methods is expected to drive the market for geosynthetic clay liners in the future.
- Geofoam: They are blocks or slabs created by expansion of polystyrene foam to form a low density network of closed, gas-filled cells. It is used as a lightweight fill or as a compressible vertical layer to reduce earth pressures against rigid walls. It is extremely light and can withstand harsh conditions. The primary function of a geofoam is to provide a lightweight void fill below highways, bridges, embankments, etc. The use of geofoams is expected to increase owing to the advantages of low cost and better environmental sustainability.
- Geocells: Also known as cellular confinement systems, geocells are three-dimensional systems fabricated from ultrasonically welded high density polyethylene strips that resemble a honeycomb structure. They are filled with non-cohesive soils which are confined within the cellular walls. The composite forms a rigid to semi-rigid structure. The depth of the geocells as well as the size of each cellular unit can vary as per design requirements. They offer characteristics such as chemical resistance, ageing resistance, high durability and inherent flexibility. They are used to stabilise and reinforce soils in the construction of roads, parking lots and building foundations.
- Geopipes: They are perforated or solid-wall polymeric pipes used for drainage of liquids or gas. In some cases, the perforated pipe is wrapped with a geotextile filter. They are primarily used for leachate collection in the case of high compressive loads. They 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, geonet-geomembrane, etc. These combinations provide benefits over individual layers by enhancing functions, increasing interface friction angles and increasing the speed of installation. They can be thermally laminated but needle punching and adhesive bonding can also be used. They are widely used for drainage, construction of bridges, tunnels, underground metro stations, railways, etc.
Geosynthetics are increasingly being used for various construction projects in the country. They offer multiple benefits in terms of cost, quality and environmental sustainability. But their use in India is still far below global deployment levels. With an increased focus on infrastructure development by the government, the outlook for geosynthetics is bright and their use is expected to grow at a progressive rate in the coming years.