Structural support specialist Groundforce Shorco is holding back the tide for contractor May Gurney on a major road improvement project near Sandwich, Kent.
The project 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.
The current phase involves the dualling of the A256 between Sandwich and the former Richborough Power Station and Groundforce Shorco has been employed to help 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” explains Chris Hatcher, supervisor with the client’s consultant, Jacobs. This meander brings the river back upon itself, and at Richborough there is only a narrow neck of land separating the stretch of the river upstream of Sandwich from and the downstream stretch as it heads out to sea.
At this point a man-made channel, known as Stonar Cut, provides a short-cut for the river so that if there is ever a risk of flooding, excess water can be diverted straight out to sea without flowing through Sandwich.
Most of the time, Stonar Cut is closed by a sluice gate located alongside the A256. As part of the road widening scheme, May Gurney is now building a new sluice gate within a sheet-piled cofferdam with the frames supplied by Groundforce Shorco.
The 13.9 m x 13.69 m cofferdam is constructed with 12.5 m long sheet piles driven 8 m below bed level into the underlying Thanet Sand bed. The excavated depth within the cofferdam is approximately 7m. In here, May Gurney is casting the new slab upon steel H-piles before casting new concrete walls for the sluice gate.
A new apron slab, to prevent bed erosion downstream of the sluice gate, is also being constructed within the cofferdam.
The sheet piles are supported at two levels. The upper level comprises four Type 8 (13.22 – 15.22 m) 1500 Series heavy duty hydraulic bracing legs with four 50 tonne MP50 Type 6 hydraulic struts. The lower level is similar except that instead of using MP50 struts, Groundforce Shorco specified 125 tonne MP125 struts to withstand the greater lateral forces bearing on the bottom frame.
Groundforce Shorco secured the £60,000 contract for the cofferdam and associated works in September 2005. According to May Gurney’s area manager Anton Roszynski “Groundforce Shorco came up with the most appropriate solution and worked with our temporary works designers to produce the optimum design”.
To speed up the installation of the cofferdam, Groundforce Shorco suggested the use of gallows brackets, fixed to the face of the sheet piles, to support the framing.
“The excavation is quite large and assembling the shoring frames insitu would have been difficult”, says Mr Roszynski. The gallows brackets therefore provided a level ‘shelf’ onto which the pre-assembled frames were quickly and easily lowered by crane.
The shoring equipment will remain in place while the concrete structure is finished and the new sluice gates installed. “We hope to have the structures built by early September and the gates in place by October 2006” says Mr Roszynski.
This phase of the East Kent Access project has a main contract value of £10.5 million and is due for completion in Autumn 2007.
