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Monster mash

GEOSYNTHETICS

Geofabrics' huge new geocomposite machine has simplified production of complex geosynthetic materials for landfill and other applications. Max Soudain reports.

Tucked away on a small industrial estate in Liversedge, West Yorkshire is a monster of the geosynthetic manufacturing world.

It is an enormous geocomposite laminator, 40m long and 15m wide including its feed rollers, and it deliver Geofabrics' products in widths of up to 6m.

Geofabrics international sales manager David Shercliff proudly says it can manufacture 'almost any combination of geotextile filters, separators, protectors, impermeable membranes, drainage cores and grid reinforcement'.

'Increasing use of larger stone from leachate drainage in landfills was one of the reasons for installing the new facility, ' he explains.

'Needle punching technology struggles to produce geotextiles sufficiently robust to contend with the point loads imposed by 40mm to 50mm crushed angular stone with up to 50m of waste above.' Non-woven geotextiles are formed by pushing barbed needles in and out of a thick blanket of polypropylene fibres, entangling them and producing a carpet-like material that offers protection, drainage and filtration.

Puncture resistance is based on the quantity of fibres used and hence the thickness of the blanket to begin with - and there is a limit to what the needle punching machine can handle.

'The new process allows two highly puncture resistant nonwoven geotextiles to be bonded together, ' Shercliff says. 'As a result, composite protectors can be made with 25kN to 40kN CBR puncture resistance - previously our highest rated product was 19kN.' He adds that the 6m wide rolls the machine can produce are not available anywhere else in the UK.

But what really brings the machine into its own is its ability to form geocomposites in one continuous process. One product in the Protexia range is described by Shercliff as 'a landfill cap on a roll'. This is basically a geotextile protector 'sandwich' filled with materials for gas venting and water drainage and a landfill capping liner.

A similar system, GPT1, was used to cap a chemical waste landfill at Bran Sands in Northumbria before construction of a waste treatment plant in 1999.

'GPT1 was originally made on a needle punch machine but caused problems with production, ' Shercliff says. 'It is now made on the laminator - it is a better way of making a better product.' 'Instead of five products or layers we have one, which obviously cuts down material cost and installation time, ' he says.

'Quality is improved and instead of testing many shear surfaces between different materials, only one has to be tested - between the material and the landfill.

'The geocomposite facility gives us the opportunity to develop a range of geotextile products that are unique - we are not trying to be all things to all men.' This philosophy has pervaded the company since it was established in 1992 by managing director Bob Warwick.

Geofabrics was set up as a subsidiary of heavy duty carpet manufacturer Heckmondwike FB to develop high-performance nonwoven geotextiles to protect landfill liners. Since then it has concentrated on this and the coastal engineering market.

'In 1992 membrane protection was a fledgling industry, ' Shercliff says. 'Usually the landfill liner was covered with a drainage medium, typically sand.

But spreading the sand often put holes in the liner, so there were obvious benefits in developing a geotextile protection layer.' Following research at Hannover University and some field trials at Risley Landfill site near Warrington, Geofabrics produced its non-woven geotextile GP (Geofabric Protectors) range.

Success quickly followed by concentrating on core sectors, says Shercliff, and in 1996 Geofabrics separated from its parent company 'giving us more control of our destiny'. Soon after, however, things took a turn for the worse.

'In 1997 we had some problems, mainly due to client mergers.

Fewer clients meant their buying power increased, which drove down prices. There was also increased competition from Europe, ' Shercliff explains.

Around the same time Geofabrics tried unsuccessfully to set up a company in South Africa.

'Because our work is seasonal, with most going on in the drier summer months, it was decided that an operation in the southern hemisphere [with its reversed seasons] would smooth out demand throughout the year, ' says Shercliff.

Unfortunately, the failure of the South African rand - it halved in value against the pound - meant the venture failed.

Licking its wounds, the firm decided to concentrate on the UK market and reinvigorated itself with the launch in 1998 of three new non-woven products - the high performance (HP), medium performance (MP) and economy performance (EP) ranges.

Shercliff says: 'The development of the economy range was driven to a certain extent by contractors who judged the effectiveness of the geotextile purely on weight.' Made from carpet waste fibres, with different lengths and widths, the range was cheaper but not as good a quality as the other ranges made from single sized prime (ie not recycled) fibres.

'We have since continued to educate contractors that it is puncture resistance not weight that should be the deciding factor in choice of fabric, ' Shercliff says.

This seems to have had some success, as the EP range was dropped in 1999 when Geofabrics launched its HPS and MPS isotropic geotextile filter ranges.

For coastal engineering, the firm supplies non-woven high performance geotextile filter separators to be used instead of granular drainage behind rock armour.

'The market has been dominated by woven geotextiles, especially from the Netherlands, ' Shercliff says, but argues that under deformation, the flow of water through woven materials falls, whereas in non-woven it is maintained.

Geofabrics has also supplied non-wovens for rail work, to help relieve water pressure built up by 'pumping' - the cyclical loading caused by passing trains.

A rail test rig for a Department of Trade and Industry sponsored test programme has been set up in another of the firm's buildings at Liversedge to examine geotextiles deformation and puncture resistance under repeated loading. This work is being carried out with industrial partners Jarvis, Aqua Geocomposites, ELS and RMC, plus Russ Tebay of Leeds University and Geotrac Rapide, the university laboratory.

'We started out with just fabrics but we rapidly moved to geocomposites, ' Shercliff says.

'These have increased strength and can release water through a preferred route.' Other research and testing is being carried out in the firm's laboratory. Set up in 1993 for quality control and product development, the lab now has UKAS accreditation and carries out a number of index tests for quality control, including CBR puncture resistance, tensile strength, cone drop penetration and water permeability.

Geofabrics has also developed tests to monitor performance under simulated site conditions.

For example, the cylinder test simulates long term loading conditions in the base of a landfill, testing combinations of stone, liner and geotextile.

Results give an indication of strains under fixed loads to give the 'protection efficiency value' Shercliff says. 'The Environment Agency has developed guidance for its work based on the test, ' he adds.

Recently, the firm has begun to venture into Europe. Further afield, it developed and supplied scour protection to the piers for the new Bhairab Bridge over the Meghna River in Bangladesh, 50km north east of the capital Dhaka (European Foundations Autumn 02).

Bangladesh is basically a delta with low-lying silty soil, where rivers may change direction and depth by up to 30m a day. The solution, says Shercliff, is to build levees and bridges well above flood levels and protect these embankments from erosion.

He says bridges are particularly vulnerable, needing long upstream and downstream aprons. For the Bhairab Bridge, Geofabrics worked with UK consultant Gibb to develop a two-layer fabric. The underside is made of coarse fibres that grip the surface and prevent erosion and piping.

The upper layer is made from finer fibres and is a filter and separator, preventing loss of fines.

Sheets of fabric were laid out on the flat river bank and sewn together with nylon threads to form 30m wide, 60m long mattresses. A square lattice of bamboo poles was then fixed to the top of the sheets and the mattress pulled into the river using two tugs. Once in position, labourers threw rock onto the mattress from small dows, slowly sinking it. Mattresses were overlapped to ensure complete coverage. The contractor for the bridge scheme is Edmund Nuttall and Halcrow is resident engineer.

Back in the UK, the geofabrics market generally follows the construction industry as a whole, says Shercliff. 'But because landfill work is directly linked to the earthmoving market, if there is a lack of large earthmoving projects like road schemes, earthmovers move into the landfill market and our work increases.' Geofabrics' reliance on its core markets of landfill, coastal and rail in the UK has reduced with diversification into other fields and countries. This will help in the face of landfill tax increases, which could see fewer waste facilities developed and a drop in demand for landfill products.

'On the other hand, increases in aggregate tax mean a drop in the use of drainage stone and this means the market for geotextile filters is improving - hence the investment in geocomposites, ' says Shercliff.

Contaminated land: the future's orange

Geofabrics came up with a colourful way of protecting and warning residents of potential contaminated material on a new housing development near Ipswich: it supplied one of its geotextiles in bright orange.

George Wimpey has nearly finished work on the houses in Martlesham. A century ago part of the site was used as landfill. Since then it has had a variety of uses, most recently as a plant and machinery storage yard for a construction company.

A ground investigation showed very light contamination. No gas was being produced, there were no dangerous substances and it was felt that the site had settled completely over the 80-100 years since its closure.

Although the risk was very low, Suffolk Coastal District Council felt that the chance of contaminated material being exposed had to be minimised. What was needed was a barrier that did not interfere with the site's natural drainage.

Geofabrics supplied its needle punched non-woven HPS3 geotextile for the job. The material has high impact resistance and strength, to withstand any attempts to dig through it, combined with 'excellent filtration and permeability characteristics', the firm says.

Unusually, the fabric was also supplied in high visibility orange to act as a warning should the material be unearthed by future residents.

The fabric was laid after George Wimpey had dug down 500mm. 'This meant we have been able to keep more material on site, rather than excavating all of the contaminated material, which would have dramatically increased our costs, ' says George Wimpey site manager Mike Hockley.

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