The piling work has been commissioned by Costain Atkins Black & Veatch (CABV) JV and its client Thames Water.
This is the second emergency job of this kind that Sheet Piling UK has handled for Thames Water, having done a similar one at Island Barns Reservoir in 2017. The same sheet piling installation methods deployed at Island Barns are being used for the remedial works to the embankment at Staines.
A sheet pile cut-off wall is being installed 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 floating barge, created from Unifloat pontoons, 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 80-tonne 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 piling contractor says that this process is kinder to the existing structure than a cement-bentonite cut-off wall, which would require extensive enabling works – the construction footprint of the sheet piling solution is far lighter, it says. This protects the fragile crest of the dam from further damage, while 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.
Once the sheet pile wall is installed, Sheet Piling UK will reinstate the clay core, after conducting pitch, tenacity and elongation tests.
The work is expected to take around 12 weeks and is expected to be carried out in line with current site operating protocols.
Sheet Piling UK managing director Andrew Cotton said: “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.”