Llyn Alaw reservoir post-tensioned anchor installation

As a result of leakage along the downstream face of the dam, a section 10 inspection carried out in February 2006 contained a recommendation for a study to be undertaken into the uplift pressures and stability of the concrete gravity dam impounding Llyn Alaw reservoir. The study was subsequently carried out and showed the dam to have inadequate factors of safety for stability during an extreme seismic event. Dwr Cymru Welsh Water awarded a contract to undertake the design and supervision of works to ensure the stability of the structure. The selected method of stabilising the structure was to install 44 no. post-tensioned strand anchors along the length of the dam, vertically through the crest and into the bedrock foundation. This paper describes the stages of the project from feasibility studies and design through to construction of the scheme, which was completed in mid-2013.