A Moorland dam - remedial grouting works

Abstract

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 934,000m3. It is one of the earliest dams constructed by Bateman and lies in a cascade of three reservoirs. As part of United Utilities (UU) Portfolio Risk Assessment (PRA) an Internal Erosion Toolbox, flood and slope stability studies were undertaken. These identified that the reservoir's primary failure mechanism was internal erosion through the embankment and presented an unacceptable risk. In order to confirm the conclusions and target a potential solution a Willowstick survey was undertaken which identified two potential seepage flow paths, one flowing into the existing outlet conduit upstream of the core and the other suggesting a compromised central core. This paper summarises the grouting works undertaken to target and 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 (QCE) 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 into the Tube-a-Manchette (TAM) installations with the works completed in June 2023, two months ahead of programme and significantly below predicted costs, enabling the local walking routes to be reopened prior to the school holidays.