Groundforce Shorco, the UK’s leading supplier of engineered shoring solutions, is providing structural support on a major reservoir improvement project in Yorkshire.
The work is being carried out by one of Yorkshire Water’s framework contractors Mott McDonald Bentley (MMB) at the Leeming reservoir near Oxenhope. It entails the enlargement of the concrete spillway which controls the water level in the reservoir. During periods of high rainfall, the spillway carries excess water away, preventing the inundation of the dam and the possible flooding of the surrounding land.
With climate change already bringing about more extreme weather conditions in the British Isles, Yorkshire Water is working to ensure its infrastructure can cope with changes in rainfall patterns. This project will ensure the 130-year old Leeming Reservoir can cope with water levels calculated for exceptional storm conditions likely to occur only once every 10,000 years.
The £1.8million main contract requires the concrete base and walls of the existing spillway to be demolished and the excavation enlarged for a wider, deeper spillway. The work is being carried out in two main phases: phase one consists of increasing the wall heights in the spillway by lining with a 300mm thick reinforced concrete liner, and phase two consists of deepening and widening the tumblebay above the spillway.
Steel Larssen sheet piles have been supplied by Groundforce subsidiary Piletec Dudley Vale to provide full earth support to the new excavation. The temporary works design is a propped cantilever with Groundforce Shorco Hydraulic struts supporting Mega Brace waling beams near the top of the excavation
“Larssen piles were chosen for their strength,” said Groundforce Shorco’s Danny Terry. “They are driven into the ground and will support the excavation without any additional propping at the base. All that’s required is a support frame at the top of the excavation.”
A significant factor in Groundforce Shorco winning the £40,000 shoring contract was the fact that it could offer a complete service, including the supply of piling hammers and sheet piles. Piletec Dudley Vale’s order for Larssen piles was worth an additional £28,000.
The shoring equipment used comprises Mega Brace walings supported by HSK80 struts and HSK80 raking struts. “The flexibility of this combination was the ideal solution for the complex dog-leg shape of this excavation”, said Mr Terry.
“It’s unusual to combine horizontal and raking struts in the same job. In the spillway, we could prop between the sides of the excavation but in the tumblebay which feeds into the spillway, there are sections with no opposing face to push off from. So here we used hydraulic raking struts fixed to the anchor points at the base of the excavation.”
Mark Porter, project delivery manager for MMB, added: “Groundforce Shorco was appointed as they had a suitable and safe system available which suited our needs to carry out construction in a safe environment and they contributed to how the construction work was carried out in the tumblebay.”
The irregular-shaped excavation is about 44 metres long with a maximum width of 14.5 metres and maximum depth of 6.7 metres. With the sides of the excavation supported with the Groundforce Shorco equipment, MMB is now casting the new concrete base and walls inside the structure. The Larssen piles will be recovered following completion of the concrete structure.
The project is on target to meet its programme and is scheduled for completion later this summer.
