A watertight solution is literally being provided at Staines Reservoir in Surrey, by Preston-based sheet piling contractor and installer, Sheet Piling (UK) Ltd, working on behalf of Costain Atkins Black and Veatch (CABV) JV and its client, Thames Water.
The emergency job is the second of its kind that Sheet Piling UK has handled for this client, with the first, at Island Barns Reservoir, completed in 2017. The same successful sheet piling installation methodologies deployed at Island Barns are being used for the required remedial works to the embankment at Staines.
The project will see Sheet Piling UK’s team installing a sheet pile cut-off wall to prevent leakage of water through the reservoir’s core. The impermeable steel sheet pile barrier will consist of 18-metre-long Arcelormittal PU32 sheet piles, which will be installed through the existing reservoir embankment’s core, using a Giken F201 Silent Piling Press.
A dynamic element will be the feeding of sheet piles from a purposely designed and constructed floating barge, created from Unifloat Pontoons. This carries the sheet piling equipment across the water and acts as a lifting platform to feed the sheet piles to the walking Giken press.
A temporary jetty, built in the form of a rectangular cofferdam of sheet piles and filled with graded granular material, facilitates the loading of plant – an 80Te crane barge – and the sheet piles set for installation, on to the floating structure. This is then floated out to the installation location, to assist the work of the low-impact Giken press on the crest of the dam.
The process is far kinder to the existing structure than a cement-bentonite cut-off wall. Whilst a cement solution would require extensive enabling works, the construction footprint of the sheet piling solution is far lighter. This protects the fragile crest of the dam from further damage, whilst also cutting the risk of water pollution by arisings and spoils that can form a slurry. Only a shallow trench is required for the walking press-in piling machinery, minimising the environmental impacts.
Once the sheet pile wall is installed, Sheet Piling UK will fully reinstate the clay core, after conducting pitch, tenacity and elongation tests.
The work is anticipated to take around 12 weeks and, due to the distances between key workers, be carried out safely and in line with the current health regulations for those having to work on emergency and essential works.
The design-life of the piles used is around 100 years, so the repairs will last a long time into the future, safeguarding this reservoir for water supply and leisure use.
Sheet Piling (UK) Ltd’s managing director, Andrew Cotton, says: “We have gained an unrivalled level of expertise in reservoir repair projects, with our sheet pile-focused solutions having proved their efficacy when water leakage is occurring at a dam. We did not expect to be called upon to handle a project like this, at this time, but given the emergency nature of the project, the work had to be tackled and the team were well-prepared to do that, both in terms of past expertise and current health and safety considerations.
“We anticipate many other such reservoir repair projects in the coming years, as Victorian infrastructures start to deteriorate, causing a variety of issues.”
