The application of geosynthetics in infrastructure is steadily gaining ground. Largely manufactured from polymeric materials, these technical textile products are becoming more popular in various infrastructure sectors and are being used to construct retaining walls and steep slopes, highways, airports, etc. They are being used for ground improvement and shore protection works as well. In the scenario of deteriorating climate conditions and increasing awareness of the need to reduce carbon footprints, these products offer sustainable solutions.
Geosynthetics are extensively used in the construction of roads and highways. They are of particular use in undertaking construction in difficult terrains such as marshy stretches and soft deposits.
When placed at the interface between the aggregate and subgrade, geosynthetics function as a separator preventing the subgrade and aggregate from mixing. They also help in controlling moisture infiltration and retardation of reflection cracks in pavement overlays beneath surface overlays. For permanent filter applications, geotextiles can be manufactured according to strict specifications. They offer enhanced consistency in installation and less susceptibility to separation during handling and placement.
Geotextiles, geogrids and geocomposites provide a sustainable option for pavement stabilisation. Along with reducing the thickness of the load-bearing layer, geogrids provide additional reinforcement which increases the life span of the road. Its usage leads to cost savings, better performance and a lower carbon footprint. Further, geogrids help in mechanically stabilising a road’s aggregate layers, in delaying early failure of flexible pavements and reducing asphalt rutting and cracking.
The country’s road sector is a major consumer of geotextiles. Woven geotextiles have been deployed in a number of projects such as road development in Daund, Pune; the Rajiv Gandhi Setu connecting Nani Daman and Moti Daman; construction of road embankments in Kerala; and construction of embankments in the IT Corridor in Chennai.
Under the Visvesvaraya Setu project, the substructure was reinforced with bi-oriented geogrids using bottom ash as a filler material. Extension of the Aligarh-Ghaziabad section of National Highway-91 in Uttar Pradesh involved the conversion of the existing two-lane highway into a four-lane one. The side slopes of the highway embankments required protection against erosion from rainwater runoff flowing down the slopes. Here, geocells were an effective way to prevent soil runoff. Geocells have also offered a viable solution in strengthening and fixing the water accumulation problem on State Highway-30.
As in the road sector, geosynthetics can be utilised for rehabilitation and strengthening of existing weak formations in the railway sector too. In addition, geosynthetics are also used for separation and reinforcement thereby arresting pumping of fines from the sub-base into the ballast in order to prevent contamination of the ballast and minimising settlement of railway tracks (loss of track alignment and level). Geotextiles coupled with geogrids provide stabilisation and reinforcement to the tracks.
The basic functions performed by geosynthetics such as separation, filtration, drainage and reinforcement assist in enhancing the mechanical and hydraulic behaviour of base structures in railway networks. Further, geosynthetics can also be used for embankment slip repairs, construction of high banks on soft soil, erosion control of slopes, track bed design, reinforcement of earth embankments (railway loading), formation rehabilitation and protection against rockfalls.
Northeast Frontier Railway (NFR) has used geogrids in combination with geotextiles and sand layers for formation rehabilitation. The performance report of a trial section has been satisfactory. For low density routes, geotextiles along with sand layers and brick soling (which is a method of laying bricks in brickwork) has been used in East Central Railway’s Sitamarhi-Darbhanga new line project.
Under the dedicated freight corridor project, due to limited right of way being available, toe walls (low wall constructed at the bottom of an embankment to prevent slippage or spreading of the soil) needed to be constructed. Though it is a common feature at railway sites, the toe walls in this case were constructed using geocells. Geocells have also been used for controlling erosion along the slopes of embankments on either side of the railway track between Govindwal Sahib and Khadoor Sahib, a single-track corridor for transportation of coal to the thermal power plant at Govindwal Sahib. Besides being cost-effective for the construction of new formations, geosynthetics in railways can be used for rehabilitating and strengthening existing formations for running trains with heavy axle loads.
In the airport sector, geosynthetics are used in the construction and extension of runways and reinforcing pavements.
For the extension of a runway or apron, various solutions employing geosynthetics are available for generating a reliable and long-lasting service life. For the construction of Pakyong airport in Sikkim, geosynthetics have been used.
Non-woven geotextiles have been used for the runway of Kolkata airport. The main issue faced here was the poor drainage as a result of the heavy monsoons. There was thus a need to minimise the erosive effect of water flowing under the pavement. The substrate comprised mixed materials (clays and sands) and featured good compression resistance.
Non-woven geotextiles capable of simultaneously serving the three purposes of separation, filtration and drainage were used to rebuild the runway. A blend of fibres of a specific linear density was used to achieve superior permeability performance of the surface. Drainage pipes were also installed every 20 metres to increase drainage capacity of the system considering the heavy rainfall.
In the port sector, non-woven geotextiles or geogrids are widely used for soil stabilisation. Geotextiles and geogrids are placed below the subgrade for enhancing the California bearing ratio and load bearing capacity of the soil, thus making it capable of handling high axle loads. Coastal areas are dynamic with unique geo-mechanical features such as soil instability and soft soils leading to a weak foundation. This creates the requirement for geosynthetics to provide soil stability.
The Directorate of Logistics, Central Board of Excise and Customs, proposed the installation of a mobile and fixed gamma ray container scanner system for the container yard at Deendayal port. Geocells provided a successful solution for improving the bearing capacity of the soft strata so that the construction could proceed since the subsoil at the port was soft marine clay.
Used in tunnel lining, non-woven geotextiles and geomembranes provide good drainage of water into the side ditches. Tunnelling contractors are experimenting with new and innovative materials including geosynthetics and geomembranes.
Non-woven geotextiles have been used in the tunnel works of the Delhi metro. Geotextiles have also been utilised in constructing tunnels in hilly terrains. In the Pir Panjal tunnel located in the Pir Panjal range in Jammu & Kashmir, geotextiles and waterproofing membranes have been used. A waterproofing system made of geotextiles was also installed in the Rohtang tunnel. The area had poor geological conditions, especially since the Beas river had earlier flowed through the planned route of the tunnel. Geotextiles have also been used to mitigate the problem of slope failures and cracks on the portals of the Chenani Nashri tunnel that occurred because of water seepage.
Geosynthetics also find a place in the construction and operation of renewable energy projects. They are used primarily for providing foundation support, stabilising concrete footings in wind and solar energy projects and construction of mechanically stabilised earth walls and slopes. Geocells have been used to mitigate the problem of exposed foundations of 20 wind turbine generators at Mandsaur, Madhya Pradesh. The reason for the exposed foundations was soil erosion due to wind and rain-water runoff. The geocells helped in preventing surface soil erosion by confinement.
Geosynthetics help save costs, enhance the lifespan of infrastructure projects and, most importantly, are less damaging to the environment. Today, the benefits provided by geosynthetics are being increasingly recognised. However, their use in infrastructure sectors in the country has not yet taken off and the potential of these products remains largely untapped. Increasing adoption of geosynthetics by players in the infrastructure space is required.
While the government is encouraging the use of geosynthetics, much more needs to be done to increase deployment. The need of the hour is to carry out requisite research and development for the use of geosynthetics in infrastructure sectors and, in particular, for specific use cases.