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Back to nature Rod Smith reports on the drive for increased use of natural fibre jute geotextiles in civil engineering projects.

The United Nations International Trade Centre of Geneva has begun a programme of promotion of natural fibre jute geotextiles in western Europe. The idea is certainly not new, with uses of natural fibre geotextiles such as reed matting dating from around 5000BC. There are also references to it in the Bible.

Soil reinforced with willow and reeds was used extensively in river bank construction along the Tigris and Euphrates in 3000BC in what is now Iraq, in Italy in the 13th to 17th centuries, along the Mississippi in the 1800s and more recently in the Dutch sea works of the 1950s. Jute appears to have been first used in the US as a geotextile laid on slopes to prevent wash-off from newly seeded grass.

Synthetic geotextiles were introduced in the 1950s, initially by textile manufacturers keen to find new uses for their polymer fibres as the decline of the western clothing and carpeting industry set in.

Since then geotextiles have seen spiralling growth (Figure 1) with a forecast by UNITC of 1,400M.m2 by the new millennium.

Europe and North America each account for 40% of this consumption with the remaining 20% attributed mainly to Japan, Asia and Australasia.

The main applications are shown in Figure 2 with the principle use still being as a separator in earthworks.

Jute accounts for less than 1% of the total geotextile market, despite the fact that it is a low-cost material and that both research and the results of full-scale use have demonstrated particular technical advantages for certain applications.

This paradox is the reason that the UNITC, with the UN Development Programme and the Jute Manufacturers Development Council, has initiated the promotion programme.

UNITC appointed my company, Elwood Consultants, a British geotechnical firm with extensive European connections, to head the launch and to bring together the differing fields of civil engineering, geotextiles and jute fibre technology.

I believe the jute industry is essentially based on textile products and has not been perceived by geotechnical engineers in Europe as relevant to their needs.

The programme intends to change this by providing product information in a form that is readily usable by engineers. I think jute will be of particular interest to owners and contractors, who would see their material costs greatly reduced.

One key concern about jute is that it typically degrades within two to four years. While this does limit a number of engineering applications, it is not as restrictive as this t might first imply.

The first major initiative under the UN programme was two seminars, which I chaired, held in London and Geneva in November last year. Representatives were invited from the jute producers, suppliers, researchers, designers, contractors and specifying auth- orities.

In the keynote address, UNDP's Ajay Prasad gave a firm commitment for support from the agency.

The events reinforced my view that while some geotechnical applications are clearly suited to jute, the material characteristics need to be much more clearly elaborated.

It was apparent that the audience was generally aware of the obvious uses, such as erosion control, but that little was known about composite products involving jute with synthetics or jute combined with coir. These are the products that have the most potential for the geotechnical community.

Another speaker at the seminar, Jane Rickson of Silsoe College, identified the three main areas of jute application to be erosion control and vegetation establishment, agroplant mulching, and rural road pavement construction.

Rickson explained how testing over 12 years at Silsoe College under a range of environmental conditions proved the technical excellence of jute compared with other natural and synthetic geotextiles.

She also identified a number of salient factors in determining the effectiveness of the geotextile: percentage cover, water-holding capacity, thick and rough fibres/yarns, the need for installation procedures which do not disturb the site, and aligning fibres/yarns across the slope orientation. Results of her field and laboratory vegetation establishment tests showed jute to be highly effective.

Professor Bob Sarsby of Bolton Institute suggested the industry would find that combinations of geotextile types would provide benefits greater than the sum of each. He introduced a newly developed wick drain formed from a jute sleeve packed with coir. Delegates were equally surprised to learn of his full-scale trials of reinforced soil walls incorporating jute rope reinforcement.

This research graphically demonstrated the strength of the jute to support wall heights of 4m and more. Sarsby also said that not enough attention had been paid to use of jute in road construction, especially over areas of poor ground, which he believed to be a potentially large application.

The microclimate regime operating around jute geotextiles has been the focus of the work by Yves-Henri Faure of Grenoble University who provided evidence for the efficiency of jute sheets in preventing loss of soil in shallow and steep slopes.

Earthworks were built on a test bed capable of being rotated to various inclinations and subjected to simulated rainfall varying from light to heavy tropical downpours. The amount of soil lost to erosion was measured. The faces were then protected by various geotextiles and the soil erosion again measured. Over the whole range of rainfall intensities and slope angle, jute geotextiles out-performed other materials. Faure commented that a jute of approximately 500g/m2 appeared to be cost-effective.

Francoise Dinger of French government agricultural research centre CEMAGREF described the performance of jute in promoting vegetation at large erosion protection sites, including high-altitude ski slopes where precipitation was significant.

Jute has the ability to absorb five times its own weight of water. This retained water first attenuates the run-off into the drainage system and is then released gradually to soak into the adjacent soil where it nourishes the vegetation.

A second effect of the jute sheet is to ameliorate the highs and lows of soil temperature and in particular to shield the vegetation from severe frosts, which again aids growth.

Continuing the theme of erosion control, Mike Hyder of Hy-Tex said prevention of soil erosion was better and more cost-effective then carrying out remedial works to eroded sites. He said the most vulnerable sites were over-steepened slopes, with exposed, easily eroded sub-soil, on disturbed or badly compacted ground.

The consequences of soil erosion are poor growing conditions, additional costs for remedial works, blocked drains and flooding, pollution of waterways and increased maintenance, he added.

'Before and after' slides from contracts demonstrated the dramatic improvement in vegetation growth and erosion control achievable by using jute.

Barbara Lois of SIRAS company described the extensive environmental works undertaken in France using jute geotextiles. These included the rehabilitation of mine dumps, restoration of the Rhone river banks and the vegetation of high-altitude steep slopes at the Winter Olympics ski jump in Savoie. Landscaping of slopes along- side the TGV rail line and along highway cuttings and embankments showed the effectiveness of the geotextiles.

According to Dr Finn Terkelsen from Denmark: 'The partners in this field are playing a waiting game. The jute mills are waiting for the civil engineers to tell them what do, while the civil engineers are waiting for the jute mills to show them what is available.'

Research has been carried out by several institutes in jute-producing countries, as well as in Europe, said Terkelsen. These produced interesting results but have not to date promoted wider use of jute. The wide gap between the producer and the ultimate user must be bridged.

SK Bhattacharya of the Indian Jute Mills Association gave the view of the producers and manufacturers. He pointed out that jute geotextiles sell in Europe for £0.40/m2 to £0.80/m2, compared to approximately £1.10/m2 to £1.35/m2 for synthetic geotextiles, and other natural fibre geotextiles which range from £0.75/m2 to £2/m2. Nevertheless use of jute remains low.

Concerns that jute degrades within two to four years were countered with comments that in practice this is long enough for vegetation growth to become established, and trials have shown that even the degraded by- products are beneficial to plants.

A new family of treated jutes takes longer to degrade, increasing the potential engineering applications of these products.

In the post-seminar discussion Dr David Mitchell described the work of Wolverhampton University Experimental Station at Hilton, Shropshire.

Here eight soil erosion plots have been established on a south-facing slope and these were used over a one-year period to compare soil erosion on sections protected by either jute geotextiles (500g/m2), rye grass, and a bare soil slope. The grass-only protected slope reduced the erosion by 54% whereas the jute geotextile reduced erosion by 99% compared with the bare slope.

Discussion moved on to the difficulties of vegetating the steep faces of reinforced soil slopes. Philip Wilson of the Highways Agency, Department of Environment, Transport and Regions, advised that the aspect of a structure had an effect on the vegetation of slopes, with south-facing ones proving difficult.

Wilson said that the Highways Agency would accept jute, but due to its biodegradability it was to be used only in conjunction with other more long-life materials in case the vegetation growth failed or was delayed. He referred to work under way at the Transport Research Laboratory and said that a report was to be published soon. Dr Ken Brady of TRL said that while there appeared to be a wealth of agro/horticultural research data, more encouragement to use jute would come about if the salient technical aspects were drawn together and published in a form useful to geotechnical engineers.

Dr Vedat Ozsanlav described the techniques developed at BTTG, Manchester, enabling jute blended with synthetic fibres to be processed on the existing non-woven production machinery. A wide range of technical products of widely varying properties and with weights from 100g/m2 to 2,000g/m2 and thicknesses of up to 60mm could be produced.

The seminars clearly helped forge links between opposing sides of industry which will be instrumental in developing the use and acceptance of jute.

They also identified the clear need for concise technical information, particularly of direct relevance to highway engineers.

I intend to ensure that the next phase of work addresses this.

Rod Smith is managing director of Wolverhampton-based Elwood Consultants.

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