A Moorland dam: remedial grouting works

Dam T was constructed around 1880 as a water supply to Greater Manchester and is a category A impounding reservoir, comprising an earth embankment with a central puddle clay core and storage capacity of approximately 934 000 m³. It is one of the earliest dams constructed by Bateman and lies in a cascade of three reservoirs. As part of United Utilities portfolio risk assessment an Internal Erosion Toolbox, flood and slope stability studies were undertaken. These identified the reservoir's primary failure mechanism as internal erosion through the embankment, presenting an unacceptable risk. To confirm the conclusions and target a potential solution a Willowstick survey suggested a compromised central core. This paper summarises the grouting works undertaken to remediate the potential core defect in a constrained and environmentally sensitive site. It highlights the benefits of collaborative working, supported by specialist contractors, the qualified civil engineer and catchment teams, the use of innovative techniques and lessons learnt from previous projects as well as the challenges presented by the proximity of the public and nesting birds. A total of 322 980 litres of grout was carefully injected with the works completed two months ahead of programme and significantly below predicted costs.