A Dense Asphaltic Concrete (DAC) lining has been completed by Walo UK for the 13th cell of the Westmill landfill site in Hertfordshire, UK.
The hydraulic engineering specialist said that it lined its first cell at the site back in 2003 and completed the latest work to create 900,000 cubic metres of landfill void in six weeks.
The Westmill site is operated by Biffa Waste Services. It receives municipal waste from the south-east region of the UK, consisting mainly of household and business waste with some construction industry waste.
The facility is located on a chalk aquifer, so environmental considerations have always been of paramount importance to the operator. WALO explained that its Dense Asphaltic Concrete is resistant to chemical attack, impermeable to leachate and methane and will withstand years of use without risk of leakage or degradation.
The company said that despite its impermeability, DAC is still very flexible and robust. This makes it particularly suitable for lining landfill cells as it can accommodate settlements of up to 10% and yet traffic can run on it immediately after laying without causing any damage.
The asphalt used in WALO’s lining system is formulated in the company’s Zurich laboratory and a site specific design is created for each project. During construction, ongoing testing of the asphalt is carried out by WALO’s on-site laboratory.
The latest cell to be lined at Westmill has a total surface area of 18,800 square metres. The works involved laying 2500 square metres of the asphalt and mastic layers by hand on the intercell bund, laying 9500 square metres by paver and winch systems to the side slopes of the cell and 6800 square metres by paver to the base.
The gradient of the side slopes was 1 in 2 with a maximum length of 60m. Once the lining works were completed, a leachate collection and removal system was installed.
The lining system to the base, side slopes and intercell bunds of the cell comprised a 500mm clay lining layer, a 200 mm sub-base material layer, a 60mm asphaltic binder layer, an 80mm dense asphaltic concrete layer and a mastic seal coat.
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