Landfill Cap with a Geomembrane

Landfill Cap with a Geomembrane

Peterhead | NAUE GmbH & Co. KG

Steep learning curve

Careful consideration had to be taken with steep sides in a landfill capping operation in Scotland. Situated just a few miles south west of Peterhead in Aberdeenshire, Stoneyhill Landfill has recently undergone a capping and restoration scheme in Phase 2 of a planned operation. SLR Consulting has been heavily involved with the project, and the company’s Darren Keogh – Principal and Technical Discipline Manager for Landfill – explained the challenges to be overcome.

Ordinarily, waste would be filled to give a gradient of one length vertical to three lengths horizontal (1V:3H). Anything steeper than that becomes problematic in terms of stability. On this site the average gradient was 1V:2.4H – and even steeper in some places (with a vertical height of 40m). This level of gradient would usually call for re-grading work to be carried out – levelling off to bring the slope down to a more manageable and safer environment. The amount of spoil that would have to be removed was substantial, and it was felt this would use up too much void space in other landfills, bringing with it a number of environmental issues including odours and unwanted leachate.

Peterhead | NAUE GmbH & Co. KG

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Darren Keogh continues: “We undertook an appraisal of the capping system and, using a traditional analysis using British Standards Codes of Practice, we managed to come up with a design that required certain para- meters to be achieved.” “When we do a normal analysis,” Darren explains, “we put in assumed figures for the cohesive angle of friction for the planned products. As this was being taken to the limit, we felt we couldn’t just rely on quoted performance values – we needed to undertake tests for confirmation.” Interface shear box testing was carried out, and these tests confirmed that the products originally considered for the work were not going to give the adequate level of angle of friction

Following the Euro Code 7 design parameters, NAUE was using a combination of its products. This eliminated the need for more costly, heavily engineered and environmentally demanding alternatives. The completed design makes use of 37,000m² Carbofol® MegaFriction – a specifically designed HDPE barrier – and Secudrain® drainage geocomposite. These products brought stability to the capping system without having to remove vast quantities of landfill material.

The geomembranes provides a complete seal against even the most toxic substances found in landfill sites. Routinely installed as a component of landfill base seals as well as caps, the geomembrane protects groundwater from contamination. Side markings on the rolls indicate proper overlap distances for the welding crews and protective edge-strips maintain a clean surface prior to welding. The high melt flow index ensures that the geomembrane is very easy to weld. Secudrain® is a three-dimensional drainage system consisting of a drainage core and at least one needle-punched non-woven geosynthetic filter layer which protects the drainage core from the ingress of soil particles while allowing the inward movement of gas and water. All layers are thermally bonded together to maintain a high shear strength.