OnSite’s lining division team helped Wessex Water (WW) to become the first company in the UK to deliver a pressure main liner to the new international standard for cured-in-place pipes (CIPP) under pressure.

The liner was installed inside a defective rising main at the company’s Christchurch sewage treatment works near Bournemouth.

WW critical sewers engineer Nathan Hand said:

“Wessex Water has been lining gravity sewers since 1984. What was different here was putting a liner in a pressure main, so it had to be able to handle internal pressures from the pumps. This meant the design and materials were very different, with a glass fibre woven into the felt to strengthen it and a special blend of resin used.”

Extensive collaboration was required to overcome some tough challenges and complete the scheme.

Paul Musselwhite, Wessex Water’s multi-functional general foreman, explained:

“What made this scheme unique was that all work was undertaken in an active sewage treatment works. It soon became apparent that an easy fix couldn’t be undertaken due to the close proximity of a storm settlement tank. Our R&M waste department came up with a solution to overland the defective pumping main to keep the local network in operation. This also allowed time for the in-house rehab team to design one of the first pressurised liners to be installed.

Both excavations were completed in very challenging ground conditions, and we worked in close partnership with the main treatment guys and local scientists.”

The project was acknowledged by the United Kingdom Society for no dig Trenchless technology (UKSTT) at its 25th Anniversary 2018 Gala Dinner & Awards Ceremony by winning the coveted trophy for the best project in the Renovation – Water & Wastewater category.

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