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Mechplant's 1500 Series

Mechplant's 1500 Series high capacity hydraulic support system has been used to support a cofferdam on construction of the new Outer Purfleet Barrage at King's Lynn, Norfolk.

The barrage forms part of the Borough of King's Lynn and West Norfolk's North Sea Haven Millennium project to regenerate Purfleet harbour on the Great Ouse estuary.

The barrage will control water levels in the newly dredged outer harbour.

Temporary support was designed by Mechplant, working with J Breheny Contractors and consultant Calvert, Brain and Fraulo.

To cope with soft estuarine alluvium and high dynamic loading caused by a high water table with a tidal range of 5.7m, the 23m long, 6m wide and 5.7m deep cofferdam was split into three sections.

Temporary bracing was needed in the 8.6m long south and middle cells to support the 17m long Larssen sheet piles forming the cofferdam.Three levels of 1500 Series bracing were used, as well as MP125 high capacity hydraulic struts for cross strutting.

The north and south cells were backfilled and topped with a capping beam and slab, while the middle cell, which houses the stoplog gates to give access to boats, has a 1m thick concrete beam, built before removing the temporary support.

The Larssen piles in the north and south cells also act as permanent piling for the barrage.

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