Dr K Rajagopal, a Professor of Civil Engineering at IIT Madras, has worked in several geosynthetics industries in India, and is an active member of the International Geosynthetics Society. He shares his views on how geosynthetics can help support the construction of roads.
What are the advantages of using geosynthetics in the roads sector?
Soft soil subgrade and water are the main culprits behind the poor performance of pavements. The thickness of the pavement is so designed to distribute the applied loads through the pavement section safely to the subgrade. If the subgrade is poor, the thickness of the pavement is larger. The water in the pavement sections can create havoc in several manners, such as high pore water pressures leading to loss of strength, loss of fine soil particles from the subgrade, etc. These problems can be safely overcome by ingenious use of geosynthetics.
The geosynthetics commonly employed in the road sector are geotextiles, geogrids and combination of these two (called as geocomposites). The geotextiles are of two types, woven and nonwoven. The woven and nonwoven geotextiles and the geogrids have potential applications in pavement constructions.
The woven geotextiles and geogrids are used as excellent separators to separate the aggregate layer and the subgrade soil to prevent the loss of good quality road aggregate into the soft soil subgrade as schematically illustrated in Figure 1. Due to the high strength and modulus of these products they hold the pavement together in case of soft soil subgrade and help in reducing the thickness of the aggregate layer. The pavement loads are distributed over much wider areas, thus reducing the stresses transmitted to the subgrade soil. This will lead to smaller settlements and lesser rutting in the pavements.
The nonwoven geotextiles are mainly used in drainage and filtration applications below the road pavements. The nonwoven geotextiles layer placed within the pavement layer at the subgrade level prevents the loss of fine soil particles from the subgrade when the pore pressures are dissipated by flow of water. The loss of fine soils (called as piping) is a major phenomenon that leads to distress in the pavements. The filtration aspect is illustrated in Figure 1. This problem is especially significant below high-speed railway tracks.
The water that enters the pavement section can be safely lead away to the side drains through the thick nonwoven geotextiles. This will lead to relatively dry conditions within the pavement section, thus leading to better long-term performance of the pavement.
Another major problem facing the flexible pavements is quick propagation of the distress in the old pavement section into the newly laid overlay.
These cracks in the new pavement are called as the reflection cracks. The reflection cracks lead to quick disintegration of the pavement due to loss of strength and seepage of rain water through the cracks. The development of reflection cracks can be controlled by placing a geosynthetic fabric at the surface of the old pavement before laying the fresh asphalt layer. The geosynthetic layer binds the pavement and reduces the spread of cracks leading to better service life.
Geosynthetics helps in preserving the integrity of the pavement section in all the above manners leading to the longevity of the road pavements. The geosynthetic-reinforced road pavements are known to have smooth and even road surface leading to better rider comfort.
Apart from the above, the approach road embankments to the road over-bridges (RoBs) can be made steeper by the use of geosynthetic reinforcement layers. This will reduce the land requirements for the construction project, thus lowering the construction cost and the expensive legal processes in acquiring the additional land for road projects.
How does the use of geosynthetics impact cost and durability?
The initial construction costs may actually reduce by the use of geosynthetics because of the reduction of the overall thickness of pavement layers. By proper design, the use of expensive natural materials like aggregates and granular soils can be reduced. This reduction in pavement thickness will speed up the construction and the related transportation costs of natural materials from the quarries. The carbon footprint can be lowered substantially by the use of geosynthetics.
Even if the initial cost of the geosynthetic pavement section is higher, the maintenance requirements will be lower due to the use of geosynthetics. Hence, the life-cycle costs are lesser for geosynthetic-reinforced pavements compared to conventional pavements.
The durability of well-designed pavements will certainly improve by the judicious use of geosynthetics as explained in the previous section.
How do you see the future of geosynthetics in India?
The future of geosynthetics is good, considering that the full potential of these innovative products is yet to be explored. Compared to several other developed and developing countries, the use of geosynthetics in India is very low. Most of the future infrastructure projects like high speed train corridors, road connectivity projects, etc., are bound to use geosynthetics due to the advantages they offer. Apart from these sectors, geosynthetics also has potential applications in irrigation canals, landfills and other water-related projects.
According to a recent government survey, the value of the construction industry is nearly Rs 6,00,000 crore. The irrigation projects are worth an additional Rs 210,000 crore. All these projects require the use of geosynthetics in some form or other representing their growth potential. As the availability of natural construction materials reduce, the usage of geosynthetics is bound to increase.
What can be done, especially from a policy perspective, to make geosynthetics gain more popularity among players in the country?
From a policy perspective, the accreditation of the use of geosynthetics in different construction projects will greatly help in their usage. These materials are to be included in more number of specifications of the public works departments, roads and railways to gain their acceptance (such as MoRTH, Railways, CPWD, etc.). As a policy initiative, the use of geosynthetics could be made mandatory where environmental and social benefits could be realised even while there is no overall economic benefit. It would also help in taking up trial projects as was done in the US and Europe in the early days of geosynthetics.
Most importantly, the engineers are to be made aware of the geosynthetics technology by way of short courses or regular courses in universities.
What are the major roadblocks hindering the widespread adaption of this technology?
Lack of awareness and total disregard for quality and safety are the main reasons hindering the use of advanced technologies in India. However, with increasing awareness of the public and NGOs, the situation is rapidly changing in the Indian construction industry. Naturally, new technologies like geosynthetics provide the answers for overcoming several construction difficulties.