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Dry me a river

CONTRACTS

STRUCTURAL SUPPORT firm Groundforce Shorco is holding back the tide for contractor May Gurney on a major road improvement project near Sandwich in Kent.

It is part of the East Kent Access scheme to improve communications and encourage regeneration of a stretch of coast from Dover north to the Isle of Thanet. The client is Kent County Council.

This phase involves dualling of the A256 between Sandwich and the former Richborough Power Station. Groundforce Shorco is helping at the point where the road crosses the River Stour at Richborough, just north of Sandwich.

'The river almost completely encircles Sandwich before flowing into the sea, ' explained Chris Hatcher, supervisor with the council's consultant Jacobs.

At Richborough a narrow neck of land separates the river upstream of Sandwich from the downstream stretch as it heads out to sea.

A man-made channel here, Stonar Cut, allows water to be diverted out to sea without flowing through Sandwich if there is a flood risk.

Most of the time Stonar Cut is closed by a sluice gate alongside the A256. As part of the road widening scheme, May Gurney is now building a new sluice gate within a sheetpiled cofferdam with the frames supplied by Groundforce Shorco.

The 13.9m by 13.69m cofferdam was built with 12.5m long sheet piles driven 8m below bed level into the underlying Thanet Sands. May Gurney is casting a slab on steel H-piles inside the 7m deep excavation in the cofferdam. New concrete walls for the sluice gate will then be cast.

A new apron slab, to prevent bed erosion downstream of the sluice gate, is also being built within the cofferdam.

The sheet piles are supported at two levels. The upper level comprises four Type 8 (13.22-15.22m long) 1500 Series heavy duty hydraulic bracing legs with four 50t MP50 Type 6 hydraulic struts.

On the lower level Groundforce Shorco specified 125t MP125 struts to withstand greater lateral forces on the bottom frame.

Groundforce Shorco won the £60,000 contract for the cofferdam and associated works in September 2005.

To speed up installation of the cofferdam, the firm suggested the use of gallows brackets, fixed to the face of the sheet piles, to support the cofferdam framing.

'The excavation is quite large and assembling the shoring frames insitu would have been difficult, ' says May Gurney area manager Anton Roszynski. The gallows brackets provided a level 'shelf' onto which the pre-assembled frames were lowered by crane.

'We hope to have the structures built by early September and the gates in place by October 2006, ' Roszynski says.

This £10.5M phase of the East Kent Access project is due to finish in autumn 2007.

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