The use of geosynthetics has pushed the quality of infrastructure projects with diverse applications and increased the strength of construction. As a polymeric material, it is used in civil and geotechnical works of roads, pavements, tunnels, highways, railway tracks, etc. There are a number of technological applications of geosynthetics that have developed over the years. These include geotextiles, geomembranes, geogrids, geonets, geowells, geopipes, geofoam, geocomposites and geosynthetic clay liners. This categorisation is based on their manufacturing procedures and physical characteristics. Their utility lies in implementing primary functions of infrastructure projects such as reinforcement, leak-proof drainage, soil containment and separation, and filtration among others. These technologies also provide resistance to ultraviolet exposure and therefore, organisms commonly found in the soil are sustained by their use. This reduces the need to process natural aggregates such as sand and gravel in construction projects, lowering their cost, construction time and consequently, their carbon footprint. Moreover, these materials are more readily available as compared to conventional construction materials and also reduce erosion, and wear and tear.
Indian Infrastructure takes a look at some of the geosynthetic technologies that are used across various infrastructure sectors…
Geotextiles, a porous polyester fabric, strengthens the soil filling and stabilisation process of civil construction projects. They provide better control on complex terrains with unstable soil structures. They ensure the longevity of pavements for a period of 30 to 50 years, while enabling faster construction. They are useful in roads, highway, railway and port projects, with roads contributing the maximum share of 70 to 80 per cent. These road projects are majorly located in northeast India. Maccaferri, a key player in the civil and geotechnical construction industry, has implemented projects in Assam for strengthening roadsides and embankments, using geotextiles to reduce landslides and floods.
Geotextiles can be further divided into woven fabrics and non-woven fabrics. While the woven type is manufactured by interlacing flat or round strands of geotextile at right angles, the non-woven type is produced through the technique of needle-punching. A permeable textile material is produced through the needle-punching process, also called filter textile.
The Ministry of Textiles (MoT) is promoting the use of geotextiles with the sanctioning of 31 related research projects worth Rs 1.08 billion. These have been initiated under the National Technical Textiles Mission, which is pushing India in the global market of technical textiles with 12 categories that include geotextiles. Further, both academia and industry players are expected to push its wider utilisation. In August 2022, the MoT also laid the groundwork for collaboration with the Ministry of Road Transport and Highways to resolve the existing challenges faced by manufacturers and contractors. They will focus on four components: research, development and innovation; promotion and market development skilling; training and education; and export promotion of geotextiles.
Geogrids and geonets
Geogrids are polymer composites of polyester, polyethylene, or polypropylene, which are mainly used for reinforcing retaining walls, gabions and subsoil under roads and highways. They are inserted between geomembranes and geotextiles, creating a filler in the embankment of soft soils and strengthening them. Apart from stabilisation, this technology is used as an overlay on asphalt, and for waterproofing and separation. Geonets have a configuration that is similar to geogrids. They are created by a continuous parallel set of polymeric ribs arranged at acute angles to one another, forming a net-like structure. Thermoplastic polymers are pressed and threads are welded together. This material is used to separate two soil types in a drainage region. With the interlocked composition, they improve the carrying capacity of the soil as well.
There are two classifications of geogrid, namely, uniaxial and biaxial. While uniaxial geogrids are used for slope reinforcement, landfill expansion projects, retaining wall reinforcement and railway embankments, the biaxial type acts as reinforcement beneath roads and foundations, transmitting the load to the underlying weak strata. Uniaxial geogrids have been used in road construction across states such as Andhra Pradesh, Assam, Bihar, Gujarat, Maharashtra, Tamil Nadu, Haryana, Uttar Pradesh and Rajasthan, among others, whereas biaxial geogrids have been used in road strengthening projects in Gujarat and Maharashtra.
Geonets have been utilised in the foundation of storm water drains and sewer lines in Dronagiri, Mumbai. The successful use of this technology has been emphasised by the United Nations Development Programme in some key districts of northeast India. For instance, it has been used for the construction of the first green road of 183 km in Goalpara, Assam. This has helped in the establishment of over 400 habitations in the district, with improvements in delta and durable road structures.
With a thickness of 0.5 mm to 3 mm, geomembranes are composed of thin continuous polymeric sheets that can regulate fluid migration. They are produced by spraying asphalt, elastomer or polymer over geotextiles. Their application is in sectors such as transportation, oil and gas, and waste management, among others. They act as liners for waste liquids such as sewage sludge and as waterproofing liners within tunnels and water pipelines. Owing to their strength, geomembranes are being widely explored, despite being more expensive per unit than other geosynthetic products. They have been used in an evaporation pond for a zinc mine in Madhya Pradesh, water reservoirs in Andhra Pradesh and Maharashtra, and as landfill and waste management material in Maharashtra, Gujarat and Karnataka.
Among other technologies are geocomposites, which are a hybrid system of two or more types of geosynthetics such as geotextile-geogrid, geotextile-geonet and geonet-geomembrane. This technology is far superior with respect to functionality, installation speed and interface friction angles compared to separate layers. They are useful in resolving issues related to drainage and soil containment, with drainage being the largest area of application. This includes civil and road construction projects, pavement base course or edge drains, trench drains, railway and road tunnels, and bridge abutments.
Geocomposites have been used to manage erosion and flooding, as well as protect the banks of the Brahmaputra river and dykes in Majuli, Assam. They have also been used in the Surat metro line project, Jafrabad (Gujarat)-Akbarpur (Uttar Pradesh) Expressway, Northern Railways and the Eastern Dedicated Freight Corridor. In these projects, geocomposites offered an effective alternative solution in place of filter media behind the retaining wall, ground improvement and slope protection work.
Geosynthetic clay liners and geofoams are other types of technologies that are gaining ground. Clay liners are prefabricated rolls, composed mainly of two layers of non-woven geotextiles, with an intermediate layer of sodium bentonite powder. They are used to line canals, storm water impoundments, wetlands, landfill liners, highways, civil construction, mines, etc., and have been used as pond liners in Jammu & Kashmir. In contrast, geofoams are blocks or slabs created with expanded polystyrene foam forming a network of closed, gas-filled cells. They are used as a light filler material, which lowers stresses on underlying soils and lateral pressures on abutments, retaining walls and foundations. Being an efficient thermal insulator, They also reduce heating and cooling costs.
There is an increased focus on efficiency and emission reduction with high construction activities taking place in India. As a result, geosynthetics are gaining traction. There is a rising demand for related technologies and production, especially in inland water transport systems, inter-basin water transfer and flood control. New tests are being conducted by the Ministry of Science and Technology, which can help estimate the optimal quantity of geosynthetics required for the maximum benefit of strength improvement. A push to use natural geosynthetics such as jute and coir instead of polymers is also being made. Similarly, IIT Hyderabad signed an MoU with the National Highways Authority of India in July 2022, to establish a Transportation Research and Innovation Hub, which will work on newer and more efficient technologies for geosynthetics.