The acceptance and deployment of geosynthetic products in India has been growing slowly but steadily. These products are man-made synthetic materials, where at least one of the components is made from a synthetic or natural polymer in the form of a sheet, strip or three-dimensional structure. Geosynthetics are versatile, highly durable materials that are cost-effective alternatives in geotechnical, environmental and hydraulic applications.
Types of geosynthetic products
Geosynthetics are available in a wide range of forms and materials, each to suit a slightly different use. These comprise a range of planar and three-dimensional structures. Within geosynthetics, there are eight main product categories – geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoams, geocells and geocomposites.
Geotextiles: These form one of the largest categories of geosynthetic materials. The use of geotextiles has grown manyfold in the past few decades owing to their property of being less susceptible to biodegradation and hence having a longer lifespan. This is due to the fact that these textiles comprise synthetic fibres rather than natural ones (cotton, wool, etc.). Besides, the ability of geotextiles to be porous to liquid flow across their manufactured plane and within their thickness (although to a limited extent) makes them preferable to other materials. However, the extent of porosity varies.
The synthetic fibres in geotextiles are made into flexible, porous fabrics by standard weaving machinery or are matted together in a random non-woven manner and can be classified into two categories – woven and non-woven. Woven geotextiles have uniform and regular interweaving of threads or yarns in two directions while non-woven geotextiles have random placement of threads in a mat that are bonded by heat, resin or needle punching.
Geotextiles are the most commonly used geosynthetic product for agricultural, construction and transportation projects. In particular, they are widely used for road stabilisation via separation and drainage in cases where the native soil beneath the road has low natural strength due to being constantly wet. However, it is important to know the nature of the soil to ensure proper selection of the geotextile. Besides, geotextiles are also found to be an economically viable option vis-à-vis other geosynthetic materials.
Geogrids: Geogrids are made from polymers such as polypropylene, polyethylene and polyester. Structurally, they have a very open, grid-like configuration with large openings between individual ribs in both transverse and longitudinal directions. These apertures, that are the key feature of geogrids, are large enough to allow for the soil to pass through from one side of the geogrid to the other. Providing tensile reinforcement of coils is the primary function of geogrids, which are used in civil engineering applications such as the construction of retaining walls, steep slopes, roadway bases and foundations, etc.
There are three key categories of geogrids:
- The original “punched and drawn geogrids” – A sheet of either high-density polyethylene or polypropylene has holes punched into it in a regular pattern and the sheet is then “drawn” or “stretched” into the finished product.
- Coated yarn – These are more flexible technical textiles in the form of grids and use bundles of fibres, most commonly polyester, as the reinforcing component that is then coated to provide protection during installation and in service.
- Geogrids made by laser or ultrasonically welding together polyester or polypropylene rods or straps (as used in packaging/shipping) in a grid-like pattern.
Geonets: Also known as geospacers, geonets are formed by the continuous extrusion of parallel sets of polymeric ribs/strands at acute angles to one another. These are stiff polymer net-like sheets with in-plane openings used primarily as a drainage material within landfills, or in soil and rock masses, with a thickness greater than that of geogrids. While the two-layer strand geonets are called biplanar, the three-layer ones are called triplanar geonets. The thickness of the ribs primarily determines the flow capacity of the net. Geonets are used exclusively in drainage applications. In the case of erosion control, the ribs in geonets act as small check dams to slow down the surface run-off, and thereby decrease the erosion potential of water. Meanwhile, geonets are also useful in the creation of drainage layers giving direction to water flow along the geonets owing to their thickness and find applications in road construction, road reinforcement, the prevention of cracking of roads, etc.
Geomembranes: A geomembrane is a synthetic sheet with very low permeability, used to control fluid or gas migration in a structure or system. These are one of the largest categories of geosynthetics, apart from geotextiles, and find utility in landfill lining, canal lining, tunnel lining, wastewater treatment lagoons, oil and gas exploration, scientifically closing waste containment areas and leachate pits, etc. Geomembranes have high puncture resistance qualities and can endure a wide range of chemicals and temperatures. Besides, they are also highly flexible and conform well to the subgrade. In comparison to traditional products such as concrete, asphalt, etc., geomembranes have proven to be far more effective. However, they come at a higher price in unit terms as compared to other geosynthetic products.
Geosynthetic clay liners (GCLs): These are rolls of factory-fabricated thin layers of bentonite clay positioned between two geotextiles or bonded to a geomembrane held together by needling, stitching or using chemical adhesives. While geotextiles offer long-lasting resistance to physical or chemical breakdown in harsh elements, bentonite’s high distension capacity and low permeability acts as an effective hydraulic seal. Besides, GCLs also have a distinctive self-sealing property helping reduce the risk of failure due to adverse field and operating conditions.
GCLs act as barriers and help prevent liquid or waste contamination. Typical lining applications of the material include use in canals, storm-water impoundments and wetlands, secondary containment, highway and civil usage, landfill liners, landfill caps, mines, etc.
Geofoams: Geofoams are typically low density, high strength materials that are used to provide a void fill below a highway, bridge approach, embankment or parking lot. It is manufactured as large, lightweight blocks by the process of polymeric expansion. These large blocks are used in multiples and contain gas-filled cells. Other applications include thermal insulation in storage tanks containing cold liquids, within soil embankments built over soft, weak soils, separations, lightweight fill, compressible inclusions, etc.
Geocells: These are three-dimensional honeycombed cellular structures made of strips of polymer sheets that form a confinement system when filled with compacted soil. Conceptually, geocells are similar to geotextiles and geogrids but have a certain amount of depth. They provide both physical containment of an infill material and load transfer. 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.
Geocomposites: Geocomposites comprise a combination of any of three geosynthetic materials – geotextiles, geogrids and geomembranes – in a factory-fabricated unit to take advantage of each product. Hence, geocomposites extract all the major properties of the geosynthetics used in one single unit at the minimum cost. The primary uses for geocomposites are separation, reinforcement, filtration, drainage and liquid barriers. The application areas are numerous and constantly growing.
Advantages of geosynthetics
Amidst rising material costs and declining maintenance funds, contractors are constantly under pressure for providing enhanced performance on an economical budget. At the same time, government infrastructure budgets are also getting stressed due to the impact of climate change and population growth. In such a situation, geosynthetics come to the rescue by offering significant economic and environmental benefits.
Going forward, the growth of geosynthetics in the country is expected to be driven by increased construction and agricultural activities along with a focus on green initiatives. Besides, geosynthetics can be used as a cost-effective solution for existing engineering challenges. Innovation in products and types of geosynthetics is expected to continue in the coming years, adding to the existing applications of these materials. However, the volatility in prices of raw materials used in the manufacturing of geosynthetics, and a lack of specified standards and awareness are major deterrents to its growth.
Nonetheless, the use of such materials can be enhanced by developing codes/guidelines related to its manufacturing and use, ensuring adequate quality checks and quality assurance of products, setting up testing and certification facilities and rationalising research and development efforts.
Given the life-extension benefits and durability offered by geosynthetics, including enhanced efficiencies, better quality and a reduction in the carbon footprint, the government is also emphasising the use of geosynthetics. For instance, the Ministry of Textiles has incentivised geosynthetics use in road construction. Besides, a special scheme for the promotion of geotextiles was launched in the north-eastern states in March 2015, with an outlay of Rs 4.27 billion. This is in line with the road construction initiative of National Highways and Infrastructure Development Corporation Limited which plans to construct about 10,000 km of roads by 2020. Despite these steps, the use of geosynthetics has not yet been fully capitalised on. The domestic market for geosynthetics is a mere 2 per cent of the global volume, highlighting the need for sensitising project developers on its advantages. With the economy poised for significant growth, geosynthetics can go a long way in acting as a key pillar in infrastructure development.