Hydraulic engineering specialist WALO UK has been back on site at Westmill, lining the site’s final landfill cell with Dense Asphaltic Concrete (DAC). This is the 13th cell WALO has lined at the site since 2003. The lining work was completed in just six weeks and the formation of the cell has created a void space of 900,000 cubic metres, which is now available for landfill.
Located to the north west of Ware in Hertfordshire, Westmill 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.
Westmill is located on a chalk aquifer, so environmental considerations have always been of paramount importance to the operator. WALO’s Dense Asphaltic Concrete (DAC) is resistant to chemical attack, impermeable to leachate and methane and will withstand years of use without risk of leakage or degradation. These qualities make it ideal for the complete containment of all materials that need to be impounded, such as landfill waste. 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.
This latest cell to be lined at Westmill has a total surface area of 18,800 m2. The works involved laying 2,500 m2 of the asphalt and mastic layers by hand on the intercell bund, laying 9,500m2 by paver and winch systems to the side slopes of the cell and 6,800m2 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.
WALO UK Ltd is a specialist in the field of hydraulic asphalt engineering, particularly in providing impermeable barrier systems for the construction and renovation of dam faces, dam cores, reservoirs, pumped storage and equalizing reservoirs, artificial lakes, irrigation systems, canals, river banks, landfill sites and coastal protection and flood alleviation schemes.
David Wilson, Managing Director of WALO UK Limited commented:
“The potential applications of DAC around the world are extremely diverse. It is an excellent solution for landfill lining as, in addition to its great strength and impermeability, it’s very thin in comparison with other lining systems so void space can be optimised.”