Stopper Specialists hold back the tide at Medmerry

Jan 22, 2014

Groundforce’s pipe-testing and flow control division, Stopper Specialists, has supplied two of its large diameter Trelleborg Mega Plug inflatable pipe stoppers to contractors working on a major new sea defence project near Selsey on the Sussex coast.

The £28m Medmerry Managed Realignment Scheme has created new sea defences inland from the coast to allow a new intertidal area to form on the seaward side. The project has been undertaken by Team Van Oord, a joint venture between Van Oord, Kier, and local contractor Mackley Construction.

Rather than try to hold back the sea the Environment Agency, as client, chose a ‘managed retreat’ which allows a designated area of marsh to flood at high tides while being exposed during low tides. 7km of earth embankment has been built inland to act as new flood defence, along with a perimeter drainage ditch and sluices in the banks to let freshwater from inland drain out to sea.

To complete the scheme a 110m wide breach in the shingle bank to had to be excavated to allow inundation of the site. Part of this process was to remove an existing outfall structure whilst maintaining the existing flood defence and so the outfall pipes needed to be closed to prevent seawater entering the site. The contractor called in Stopper Specialists to close the pipes using two of its 700 – 1600mm Trelleborg Mega Plugs. These are large cylindrical inflatable plugs some 2.5m long and up to 1.6m in diameter when inflated.

"They are simply lifted into the pipes and inflated to a pressure of 1bar which is enough to seal them in place and withstand the water pressure in the pipe", says Stopper Specialist Technical Sales Representative, Matt Maidment. The plugs are made from tough aramid and Kevlar reinforced rubber with a heavy duty steel core and are designed to create a secure seal quickly and safely.

"These are actually not the largest in the range", says Matt. "We also offer models capable of stopping pipes of up to 2.4m in diameter." Team Van Oord project manager Tony Battrick said that without the Mega Plugs, progress on this element of the job could have been much slower. "We had two solutions: the conventional one of blocking the pipes with masonry or this one, which of course was much quicker.", he says.

The Mega Plugs were lifted into place with a tractor-mounted loading crane and then inflated with a compressor before closing the isolating valves to keep them at the correct pressure. "Once in place, they require no maintenance beyond a daily visual inspection", says Matt. The plugs remained in place for one week, during which time they kept seawater out of the site whilst the excavation of the breach took place.

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