One of the innovation in the field of civil engineering is the introduction of geosynthetics, which are turning out to be good alternative for the conventional designs and replacement, to some extent, for the scarce raw materials like cement and steel. Basically, they are artificial fabrics used in conjunction with soil as an integral part of a man made project. The term geosynthetics is generally used to designate a wide range of polymeric products used to elucidate civil engineering problems. However, their use is quite novel in the construction engineering and increasing every year in various segments such as bolstering of fill, controlling of pore water pressure, foundations and pavements. The main advantages associated with the utilization of geo-synthetics are cost effectiveness, easy and rapid installment and possibility of controlling the quality being as the products can suitably designed and manufactured in the factory.
The Geosynthetic segment comprises of technical textile products used in geotechnical applications pertaining to soil, rock, earth, etc. However, geotextiles, as these geosynthetics are commonly callued, specifically refer to fabric or synthetic material, woven or non-woven, which can be used with geotechnical engineering material. In laymen’s phraseology, the terms “Geosynthetics” and “Geotextiles” are often interchanged which occasionally leads to misperception. “Geotextiles” are actually a type of product under Geosynthetics.
Since geo-synthetics or geo-synthetic materials are planar and polymeric (synthetic or natural) materials used in contact with soil/rock and/or any other geotechnical material, for filtration, drainage, separation, reinforcement, protection, sealing and packing, they are now considered indispensable and requisite for an economical solution in these multiple functions. Geo-synthetics are especially useful in the situation of increasing land scarcity, increased consciousness of seismic menaces, and necessity of more rigorous environmental guidelines especially in the context of India. The major applications of geo-synthetics comprise civil engineering works (roads and pavements, slope stabilization and embankment protection, tunnels, rail-track bed stabilization, ground stabilization, drainage, etc.), marine engineering works (soil erosion control and embankment shield, breakwaters) and environmental engineering (landfills and waste management). India has huge demand of these sectors worth more than Rs 6 L crores. This segment primarily represents the growth opportunity for geo-synthetics along with urban development (Rs 1.2L crores) and irrigation (Rs 2.1L crores). However, its usage is very limited in the India and it makes up a demand of only 100 million square meters as compared to 4.7 billion square meters worldwide. In 2008 and 2013, the demand for geosynthetics in India was about 56 million m2 and 100 million m2 respectively, which is expected to rise to 178 million m2 in 2018. Of this, geotextiles demand is projected to decrease as a fraction of overall demand from 66% to 63% by 2018 (Table 1).
Construction aspects of geo-synthetics
The four main synthetic polymers most widely used as the raw material for geotextiles are – polyester, polyamide, polyethylene and polypropylene. The oldest of these is polyethylene which was discovered in 1931 by ICI. Another group of polymers with a long production history is the polyamide family, the first of which was discovered in 1935. The next oldest of the four main polymer families relevant to geotextile manufacture is polyester, which was announced in 1941. The most recent polymer family relevant to geotextiles to be developed was polypropylene, which was discovered in 1954.
– Polyamides (PA): There are two most important types of polyamides, namely Nylon 6 and Nylon 6, 6 but they are used very little in geotextiles. The first one an aliphatic polyamide obtained by the polymerization of petroleum derivative e-caprolactam. The second type is also an aliphatic polyamide obtained by the polymerization of a salt of adipic acid and hexamethylene diamine. These are manufactured in the form of threads which are cut into granules. They have more strength but less moduli than polypropylene and polyester. They are also readily prone to hydrolysis.
– Polyesters (PET): Polyester is synthesized by polymerizing ethylene glycol with dimethyl terephthalate or with terephthalic acid. The fibre has high strength modulus, creep resistance and general chemical inertness due to which it is more suitable for geotextiles. It is attacked by polar solvent like benzyl alcohol, phenol, and meta-cresol. At pH range of 7 to 10, its life span is about 50 years. It possesses high resistance to ultraviolet radiations. However, the installation should be undertaken with care to avoid unnecessary exposure to light.
– Polyethylene (PE): Polyethylene can be produced in a highly crystalline form, which is an extremely important characteristic in fiber forming polymer. Three main groups of polyethylene are – Low density polyethylene (LDPE, density 9.2-9.3 g/cc), Linear low density polyethylene (LLDPE, density 9.20-9.45 g/cc) and High density polyethylene (HDPE, density 9.40- 9.6 g/cc).
– Polypropylene (PP): Polypropylene is a crystalline thermoplastic produced by polymerizing propylene monomers in the presence of stereo-specific Zeigler-Natta catalytic system. Homo-polymers and copolymers are two types of polypropylene. Homo polymers are used for fibre and yarn applications whereas co-polymers are used for varied industrial applications. Propylene is mainly available in granular form.
Both polyethylene and polypropylene fibres are creep prone due to their low glass transition temperature. These polymers are purely hydrocarbons and are chemically inert. They swell by organic solvent and have excellent resistance to diesel and lubricating oils. Soil burial studies have shown that except for low molecular weight component present, neither HDPE nor polyethylene is attacked by micro-organisms.
– Polyvinyl chloride (PVC): Polyvinyl chloride is mainly used in geo membranes and as a thermo plastic coating materials. The basic raw materials utilized for production of PVC is vinyl chloride. PVC is available in free- flowing powder form.
– Ethylene copolymer Bitumen (ECB): Ethylene copolymer bitumen membrane has been used in civil engineering works as sealing materials. For ECB production, the raw materials used are ethylene and butyl acrylate (together forming 50-60%) and special bitumen (40-50%).
– Chlorinated Polyethylene (CPE): Sealing membranes based on chlorinated poly ethylene are generally manufactured from CPE mixed with PVC or sometimes PE. The properties of CPE depend on quality of PE and degree of chlorination.
Recently, with the advancement in the polymer chemistry, new innovative materials may be used as geosynthetics for civil engineering applications. These will include metallocene catalyzed polypropylene, graphene, nanofiber (nanoparticulate carbon black and carbon nanotubes) based geosynthetics, etc.
Geosynthetics are designed in many categories, depending upon its end use. They are permeable synthetic materials made of textile materials, usually from polymers such as polyester or polypropylene. The three main categories of construction of geosynthetics are – woven fabrics, non-woven fabrics and knitted fabrics. Apart from these three main types of geotextiles, other geosynthetics used are geonets, geogrids, geo-cells, geo membranes, geo composites, etc. each having its own distinct features and used for special applications as mentioned in Table 2.
Demand for geosynthetic materials is associated to the applications in which they are used. In 2016, geotextiles represented 47% of world consumption, which is 3.8 billion meters. Nearly 87% of these are used in road building or similar transportation applications. Geomembranes account for over 24% of the 2016 world market by value, but slightly less by volume. Its principal use (58%) is in roofing for buildings. Waterways, like canals, meanwhile account for the majority of consumption of geocomposites (65%) and geosynthetic clay liners (72%). Geomembranes for all applications will slightly increase market share across 2016-2021, with geotextiles and geowalls declining slightly. Geogrid, geocomposites and clay liners will maintain their relative market shares against a backdrop of steady expansion for the wider market.
Geosynthetics should be designed in such a manner that they are able to fulfill the basic functions, such as separation, filtration, drainage, reinforcement and barrier. In addition, geosynthetics should also serve the functions of protection or cushioning and surficial erosion control.
Historical background of use of geosynthetics in India
In the gigantic waterfront areas of Kerala, it has been an age old tradition to spread coconut leaves on the ground before gravel/aggregate is laid over a road formation. Nature itself exercises control on erosion through vegetation, more precisely by the fine well spread roots which support the plant upright, and also hold the soil together).
Geo-textiles and related materials, now termed as geo-synthetics were presented for the first time to Indian engineers by the Central Board of Irrigation and Power in 1985 when they organized the first National Workshop on Geomembranes and Geotextiles. Subsequently, the theme began to be frequently debated at numerous Indian Geotechnical Conferences and indigenous understandings commenced to be exchanged. Textile manufacturers instigated to diversify their merchandise range to include geotextiles. The first state-of-the-art volume on “Use of Geosynthetics in India-Experiences and Potential” was brought out by the Central Board of Irrigation and Power in 1989 (Rao and Saxena, 1989). This was a compilation of the field trials in the country, which helped civil engineers to gain assurance in the use of geotextiles. Several academic and research institutions particularly Indian Institute of Science, Bangalore; Indian Institute of Technology at Delhi, Kanpur, Bombay and Madras; Central Building Research Institute, Roorkee; Central Road Research Institute, New Delhi; Research and Designs Standards Organization, Lucknow; Gujarat Engineering Research Institute, Vadodara, and numerous other renowned organization and academic institutions have started focusing attention on manufacturing aspects and applications of geosynthetic material. The successful installation of varied geosynthetic materials in the civil works opened the market and the challenge was initially accepted by various government authorities such as the Indian Railways; Indian Navy (Nhawa Sewa Project, Mumbai); Calcutta Port Trust, Calcutta; Uttar Pradesh Public Works Department, Delhi Administration; the ministry of Surface Transport (Roads Wing) ADB projects on NH-1; etc. The Government of India also sponsored various research schemes through the Central Board of Irrigation and Power, Department of Science and Technology and the Ministry of Surface Transport (Roads) to promote the utilization of geosynthetic materials for varied applications. The Bureau of Indian Standards has also tried to standardize the testing procedures and to bring out design guidelines.
As far as recent scenario is concerned, with the newsworthy prominence on infrastructure advancement, geo-synthetic in India have established a tremendous improvement. It has been comprehensively used in the pavement of the North-South and East-West (NS-EW; 7,142 km) corridors and Golden Quadrilateral (GQ; 5,486) of the National Highways Development Project (NHDP) project of National Highway Authority of India (NHAI) (Figures 1 a, b, and c). NS-EW is the largest ongoing highway project in India. It is the second phase of the National Highways Development Project (NHDP), and consists of building 7300 kilometers of four/six lane expressways connecting Srinagar, Kanyakumari, Porbandar and Silchar, at a cost of US$12.317 billion (at 1999 prices). As of 28th February 2017, 6,549 of 7,142 kilometers project has been completed.
Innovative geosynthetic-based recent civil constructions in India
Expanding NH-48 from Ahmedabad to Vadodara: National Highway – 48 (NH-48) extends from Mumbai to Delhi, India’s biggest metropolitan cities. Along the route it also connects two major cities in the state of Gujarat – Vadodara and Ahmedabad. The National Highway Authority of India (NHAI) initiated this project to expand the ~100 km stretch to six lanes. The project included 45 crossovers where the highway traverses over internal roads of towns and villages as well as three railway crossings. If the authorities have used the conventional methods for designing the crossovers, the project cost would have shot up significantly and the construction of these walls by conventional methods was also extremely time-consuming. In contrast, reinforced soil structures were faster to construct and cost effective too. The basic principle was to construct two parallel reinforced soil structures retaining earth backfill in between. The reinforced soil walls were constructed with locally available non-plastic soils, and polyester knitted geogrids as soil reinforcement. The fascia comprised of precast segmental concrete blocks. The construction also needed to be executed in congested conditions with high-ground water table for which the civil engineers performed ground improvement measures such as replacement of poor foundation soil and placed a non-woven geotextile before the reinforced soil structure and back-fill began. The utilization of geosynthetics has saved 40% of the cost compared to the RCC walls and the project was well completed in time and has been now open for traffic.
Restoration of damaged roads at Kedarnath temple: The Kedarnath Valley has always been affected by soil erosion due to bad weather conditions. This erosion was worsened by exceptional flash floods in June 2013. Landslides and mudslides caused by a distressing cloudburst emaciated the area. The shrine was closed to pilgrims for one year during which it was necessary to clear the debris and to re-establish ground stability of the area before permitting pilgrims through again. The Government of India had a challenging task to stabilize the ground in the area within a very short time with the help of innovative and proven solutions. With the help of Nehru Institute of Mountaineering and Strata Geosystem Private limited, this emergency problem was solved in the limited time period.
The sub-soil being of very low CBR, it was possible to construct a road with a soling of cobbles and good quality aggregates using traditional method but it was an extremely tiresome and time-consuming task. It was recommended to use geocells for constructing the access road and pavement from the helipad to the temple. The geocells were infilled with local infill material (GSB). The installation was rapid, cost effective and aesthetically pleasant.
Installation of geocells at the slope near railway track to prevent soil erosion: The railway link between Govindwal Sahib and the nearest railway station, Khadoor Sahib is a single track corridor for conveyance of coal to the thermal power plant at Govindwal Sahib. Since this controls the life-line of the power plant, the rail link desires to be kept fully operational throughout the year. The link navigates through cuts with embankments on either side. While the slopes of these embankments are fundamentally stable, erosion along the slopes posed operational problems. The slopes comprise of silty fine sands which, during strong winds or monsoons, deposits onto the tracks and disrupt rake movement. The clearing of the track was time consuming; hence, an engineering solution was sought to resolve this issue permanently and keep the track functioning 24 X 7 for the power plant.
Utilization of geosynthtic material, geocell was proposed over the slopes with infill material (soil), which prevented it from sliding and eroding. Once confined, the in-filled soil would allow vegetation to grow fast and ensure a stable system which would not be affected by any agents of erosion.
Designing of India’s First Vertical Landfill at Vapi: The city of Vapi in the state of Gujarat, India, has a deep industrial history, with chemicals, pesticides, dyes, textiles, and other sectors active in the municipal area. A large volume of waste is generated every day by these industries. To meet with the environmental challenges of the city, a vertical landfill was designed to incorporate the solid and the toxic waste and make the city environment free from industrial pollution. The construction of landfills is tremendously complicate because it is a complex, multidimensional system. It is designed to protect the ground and surroundings from contamination. It takes years to plan and design a landfill, which is loaded with variety of material waste including toxic materials. They are typically divided into areas called “cells” which are designated areas for storing the waste.
Vapi Green Enviro Limited (VGEL) is involved in storing industrial waste from neighbouring industries. Conventionally, landfills are constructed with containment dykes with side-slopes, and filled with waste within the containment. However, this conventional method was found to be expensive and an impracticable option. Hence, a containment system with a reinforced soil lean structure was thought off which could generate more space. This vertical expansion was made possible without the need for a capacious earth retaining structure. The landfill was divided into cells, and each cell was filled one at a time. The first three cells were closed and covered as per legislative requirements. For the covering of the fourth and probably the final extended cell, two strategies were utilized – one in which the inner slope that bordered the landfill consist of polyester geogrid fascia wrapped around soil bags. This face was draped with a composite of geomembrane and nonwoven geotextile to prevent landfill leachate from seeping into the containment. Further, in order to deliver a maintenance-free structure, an aesthetically pleasing outer portico using precast segmental concrete modular blocks, in connection with the internal geogrids comprises of the face of the wall, providing a “fortress” look to the structure. The project has been successfully completed on 30th March, 2017.
Conventionally, landfills are constructed with containment dykes with side-slopes, and filled with waste within the containment. However, this conventional method was found to be expensive and an impracticable option. Hence, a containment system with a reinforced soil structure was thought off.
Geotextiles and related products or geosynthetics as they are now called, are now being increasingly used the world over for every conceivable application in civil engineering, such as construction of roads, foundations or earth and earth retaining structures. India is also gearing up in the field of utilization of geosynthetic materials for better life and stability of the construction works. India will have to enhance the use of geosynthetics in various government sponsored and controlled projects in diversified areas to cope up with the development in the civil engineering works.
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Dr. Bipin J Agrawal, Professor with the Department of Textile Chemistry, Faculty of Technology & Engineering at The Maharaja Sayajirao University of Baroda. He has 76 publications in Reputed National/International Journals and have presented Research Papers in 59 National/International Conferences/Seminars/Refresher Courses etc. He has written 6 chapters for four books, one of which is published by Wiley Publications. He has been associated with ALL INDIA COUNCIL OF TECHNICAL EDUCATION as an Expert Committee Member for Accreditation of various Textile Institutes all over India. He has completed three Research Projects financed by UGC, AICTE and The M. S. University of Baroda respectively and at present he is undergoing a project under DST-PURSE scheme. He is an Associate of the Textile Association of India and has been awarded Fellowship by six renowned Association/Organizations. He is associated with NSS activities as a Program Officer for The M. S. University of Baroda. He is also the President of the Alumni Association of Textile Chemistry Department of The M. S. University of Baroda.