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SMOOTH OPERATOR

GEOENVIRONMENTAL ENGINEERING

Tough legislation is forcing landfill designers to incorporate artificial geological barriers in steep-sided landfills. Rodney White says he has the solution.

Most landfill engineers and designers have, at some point in their careers, had to grapple with the twin demands of protecting soil and water and containing landfill gases.

Legislation in the shape of the Landfill (England and Wales) Regulations 2002 (Schedule 2) looks likely to create further problems for future landfills, requiring an artificial geological barrier to extend not only across the base, but all the way up the sides of steepsided landfill sites.

Many of these landfills are in worked-out quarries whose natural geology - sand or fissured rock - does not provide sufficient attenuation to prevent potential contamination risk to groundwater.

This requires installation of an artificial geological barrier at least 500mm thick, which typically means using a combination of clay and sand with geosynthetic reinforcement.

While the regulations do not stipulate that the artificial liner between the artificial geological barrier and the waste must extend up the sides of the landfill, this is likely to be required on the basis of site-specific risk assessments.

There were only a few, proven steep wall lining systems in use in the UK before the introduction of the regulations, and these will now have to be reassessed for their ability to accommodate artificial geological barriers.

Creating such barriers against the steep slopes of a quarry poses a real challenge for landfill engineers. However there is already a cost-effective solution that not only enables the rapid formation of steep smooth sides to quarry walls, but optimises waste disposal and allows geosynthetic liners to be laid with the minimum risk of damage.

It is a reinforced soil system with expanded polystyrene (EPS) facing, patented by my company, Cordek, as Tipform, and developed with Adrian Needham, now technical director of Edge Consultants, and some of his former colleagues.

The system has been used at a number of landfill sites in England and Ireland over the last 10 years. A key feature is its ability to include a low permeability artificial barrier - compacted clay or bentonite-enriched soil - within the soil backfill behind the EPS facing.

The EPS facing provides a smooth planar surface, ideal for placing the geomembrane liner and the other geosynthetic drainage, slip and protection layers of the artificial lining system.

This helps reduce the cost of laying the membrane while boosting its life expectancy and minimises the risk of damage and leachate contamination of the water courses. Flexibility in slope angle and site geometry means the system can be tailored, at relatively low cost, to schemes already under way.

Site-specific designs are needed to take account of the effects of the low permeability barrier on the reinforced soil design, and the type of reinforcement to prevent formation of preferential drainage paths along the reinforcement.

But, as Adrian Needham points out, to ensure satisfactory performance of the structure, it is important that the methods used on site adhere to the established specification to achieve proper construction of the reinforced soil wall.

Landfill, incineration and other forms of waste disposal are all held up by their adherents as the most environmentally-friendly and costeffective solution. As the debate continues, the tried and tested landfill facility will remain an essential waste disposal option, despite the problems of access, the rising cost of land and public opposition.

All those responsible for designing, operating and managing landfill sites can take heart.

The technology exists to allow proper adaptation of sites and to facilitate the construction of new ones more quickly and cheaply than before.

Rodney White is co-founder and managing director of Cordek, manufacturer of expanded polystyrene products for the construction industry.

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