Geotextiles belong to a class of technical textiles that have varied applications in geotechnical engineering. The engineered fabric improves soil behaviour through separation, filtration, drainage and reinforcement. Developed countries invariably use geotextiles made out of man-made fibres in road construction, for control of erosion, consolidation of soil and stabilisation of slopes. In India we have the advantage of abundance of jute fibres supported by an industry that has century-old experience in making of any type of jute fabric, besides providing sustenance to about 4 million people directly and indirectly.

Jute Geotextiles (JGT) and its technology
Jute geotextiles is a natural variant of man-made geotextiles and used in the same way as its man-made counterpart the technology which is accepted all over the world. Extensive studies and experiments have been conducted on JGT in technical institutions in India (e.g. IITs in Kharagpur, Delhi, Roorkee and Mumbai as well as Bengal Engg. & Science University) and abroad (e.g. Singapore State University, Bangladesh University of Engg. & Technology, Cranfield University, UK).

The purpose of using geotextiles in road construction is to strengthen the sub-grade for ensuring both longer life of the pavement and economy. Geotextiles—be it man made or natural—act as a separator between the sub-grade and the base course of the pavement overlying it, prevents migration of the top soil particles, and helps dissipate development of overpressure by draining off water across and along its own plane. The aforesaid functions help consolidate the soil without extraneous mechanical intervention. Soil consolidation being a time-dependent process, the road sub-grade becomes self-reliant with the passage of time. Usual period of such consolidation, as observed in laboratory studies and field trials, is 1-2 years at the most, depending on the type of soil and nature and intensity of traffic.
In fact, all geotextiles act as change agents to the soil on which it is laid for the initial period of 1-2 years after which use of any geotextile is redundant. JGT scores over man-made geotextiles due to its eco-concordance, price competitiveness, excellent drapability (the best among all geotextiles when wet), high initial modulus and roughness co-efficient. It has been established after extensive field trials that improvement of CBR percentage of the sub-grade is minimum 1.5 times its control value. As soil consolidation is a protracted process, improvement in bearing capacity of soil may continue for several years. In some cases, CBR value is seen to have increased even more than three times its control value after a lapse of 6 years. The higher CBR implies a lesser thickness of pavement. The cost of JGT is thus partially or fully compensated.   

When mechanism of functioning of geotextiles as indicated is considered, bio- degradation of JGT is not a technically discouraging factor. Jute can be treated suitably with an eco-friendly additive to last for two to three years and thus help achieve the desired consolidation of the sub-grade. IIT Kharagpur has recently identified such an additive and conducted durability studies on jute fabric in a research project assigned to the institute by the National Jute Board under Jute Technology Mission launched by the Union Ministry of Textiles.

Jute geotextiles can also add to the stability of road embankments. Appropriately designed jute geotextiles can be inserted within an embankment at different levels to control settlement and rotational slides. Additionally, the embankment slopes, which are vulnerable to erosion, can be overlain by open weave jute geotextiles to reduce the velocity of surface run-off after the rains and entrap the detached soil particles. Jute facilitates growth of vegetation. On bio-degradation of the fabric, vegetation can grow on the slope to control soil detachment. This is in fact a bio-engineering measure that is being increasingly favoured in the developed countries for controlling surface soil erosion with obvious environmental advantages. The World Bank is supporting such measures.

It has been observed in laboratory experiments conducted in Jadavpur University that the loss in strength of JGT is compensated by the gain in strength of the soil body. This means that the rates of the two contrasting phenomenon, i.e. degradation of JGT and improvement of soil, are in consonance. Sub-grade in a road draws its strength from separation and membrane effects principally. Pore water pressure is relieved as a result of concurrent filtration and drainage functions by JGT, which was also used as a capillary cut-off in the pilot project to prevent ingress of water from below.

Pilot project with JGT in rural roads
The National Jute Board (NJB), the promotional body under the Ministry of Textiles, Government of India (erstwhile Jute Manufactures Development Council), upon a pilot project under PMGSY with the support of Ministry of Rural Development, National Rural Roads Development Agency and the Ministry of Textiles in December 2006. The Central Road Research Institute (CRRI) was appointed as the technical consultant. The project was spread over five states (Assam, Chhattisgarh, Madhya Pradesh, Odissa and West Bengal). Ten roads, two in each state, were decided to be constructed with JGT to study its effectiveness as separator, filter, drainage medium and reinforcing material. The main objectives of this pilot project were to evaluate the beneficial effects of the use of JGT in all its three major functions and standardise different types of JGT for different applications in road construction.

Detailed project report for each of these roads was prepared by CRRI. The project roads were constructed by the respective state agencies (State RRDAs and PWD). CRRI was entrusted with the job of quality management and third-party random quality checking and performance evaluation. STUP Consultants Pvt. Ltd. was engaged as the supervision consultant by the National Jute Board to ensure quality control over the works.

Ultimately, out of the 10 sub-projects, the one in Hooghly district of West Bengal could not be taken up due to unworkable site conditions. The road remains perennially water logged. All the remaining nine roads have been completed. The road length in Jajpur district of Odissa, however, had to be reduced to 2.70 km (instead of 4 km) owing to land problems.

CRRI has completed the exercise on performance evaluation of five roads, viz. two roads in Assam, one road each in Chhattisgarh, Madhya Pradesh and Orissa. CRRI monitored performance of the five roads for more than 18 months from the date of completion. It has also taken measurements (Benkelman beam deflection test, DCP test) on the five roads to evaluate performance of the pavement proper. CRRI has finally commented that the performance of all the five roads designed with lesser thickness with JGT is similar to pavements designed as per IRC: SP 20: 2002 for rural roads without use of JGT.

JGT samples were also exhumed and taken to the Institute of Jute Technology Kolkata for tests to observe the extent of degradation. It was observed that the tensile strength of the fabric got reduced by about 20 to 30 per cent after 11 months and by about 70 to 90 per cent after 23 months. Despite progressive de-gradation of JGT, the pavement performed satisfactorily that JGT or any geotextile act as a change agent to the soil (in the instant case, sub-grade) for a limited initial period by which time the soil progressively gains strength and ultimately becomes self-reliant as a result of development of effective stress within the sub-grade.

Gist of other salient case studies
JGT has been and is being applied in many roads — mostly low volume roads — for improvement of sub-grade with success all over the country. A synopsis of case studies in some roads constructed with JGT under varying climatic, geotechnical and loading conditions is presented below.

Re-construction of a damaged road on soft marine soil at Kakinada Port, Andhra Pradesh (case study by CRRI)
• Objective: Minimising post-construction settlement, lateral dispersion of fill by use of JGT
• Soil composition: Mainly clay up to a depth of 4 metres
• Year of reconstruction with JGT-1996
• Results: After 7 months, the shear strength of the sub-grade ensured the desired factor of safety.
• Water content, void ratio and compression index decreased while dry density and CBR value of the sub-grade increased substantially (nearly 3 times the control value after 7 years)
• The road is in excellent shape after more than 10 years after its re-construction.

Internal road in Kandla Port, Gujarat (case study by CRRI)
• Objective: Mitigation of the problem of settlement due to intermixing of sub-grade and sub-base in apportion of the road by use of JGT
• Year of construction: 1997
• Results: Rut depth was minimised and other visual signs of distress were eliminated
• Settlement of the test section was compared to conventional pavement construction with increment of extraneous load from 0.5 tonne/sq. m. to 2.0 tonne/sq. m. at 0.5 tonne/sq. m. per month 3 months. Negligible settlement was observed with no visible signs of distress.

International project on JGT
Currently an international project on JGT for application in rural roads have been taken in hand with the financial support of the Common Fund For Commodities (CFC), Amsterdam, a financial institution of the United Nations, with the support of the Government of India and Bangladesh. NJB is the PEA of
the project.

The project envisages 16-field applications in India and 10 in Bangladesh. All the works in India have been completed and those in Bangladesh will be completed latest by a couple of months. Out of 26 field applications, 12 applications are in low volume roads (7 in India and 5 in Bangladesh). Performance is being monitored at regular intervals. The outcome will be known at the end of the project (in 2015). Interim measurements conform to previous results.

Standards on JGT
In the annual session of the Indian Roads Congress 2011 in Lucknow, a state-of-the-art report (Special Report 21) on application of JGT prepared jointly by CRRI and NJB was released. BIS standards on rural road and river bank erosion control applications (IS 14715: Part I and Part II: 2013) have also been published, besides a standard on guidelines for slope erosion control with JGT (IS: 14986:2001). The Indian Roads Congress has permitted the use of JGT in roads as an innovative engineering material provisionally.

Availability and quality assurance of JGT
The composite mills in West Bengal are capable of manufacturing jute geotextiles meeting the specifications of end users. These mills will assure availability of jute geotextiles.

There exist full-fledged testing facilities in department of jute and fibre technology, Calcutta University and Indian Jute Industries’ Research Association in Kolkata. NJB offers its free services for design and quality assurance of jute geotextiles ordered by end users.

Conclusion
More than 50 field applications with JGT in roads in India have been so far undertaken with remarkable improvement in CBR value (measure of bearing capacity of soil) of the sub-grade. Extensive laboratory studies in engineering and research institutes of India and abroad have been and are being carried on JGT. Besides, JGT fits in with the current global trend to use such materials in constructions as would ensure reduction of carbon footprint.

Jute products are a major foreign exchange earner and play an important role in the national economy. Jute provides sustenance to at least 5 million people of the country directly and indirectly. Jute industry is struggling for survival in view of the ingress of artificial polymeric materials in the sack-market. It is time to support JGT to the extent technically permissible in geotechnical applications for the sake of a cleaner environment and larger national interests.

Acknowledgement
The author acknowledges the contribution of N. K. Mukherjee of the National Jute Board in preparing the article.

Authored by__

Tapobrata Sanyal,
Chief Consultant, National Jute Board,
Ministry of Textiles, Govt. of India