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Gallows brackets and restraining chains were fitted to keep the frame suspended at the correct level before and afer the hydraulic load was applied.

To support the widest part of the frame Conwel l Contracts instal led an 80 tonne capacity 7 m long HSK hydraulic strut. This created a right-angled triangle between the two longest Mega Brace legs (13 m and 18 m respectively) with the right angle between the 13 m leg and the hydraulic strut. Working strut design load was 800 kN for a calculated maximum strut load of 760 kN.

This configuration meant that the angle between the longest leg and the hydraulic strut was very acute – 45°. “With the strut acting at an angle to the beam, there were considerable shear loads,” says Liam Brew. “But our standard shear clamp is designed for this and so no special atachments or welding was required.”

After completing the top frame, Conwell finished the excavation, installing another Groundforce frame to support the lower level at 2.5 m below ground level. Maximum dig depth was approximately 4.5 m at 49.125 m AOD.

“Using a proprietary support system not only made installation quick and easy but also gave us the flexibility to create a clear working space within the excavation,” says Joe McFadden. “You can’t always put the supporting struts in the most obvious position because they span the excavation and can create an obstruction. Groundforce’s design had to take the eventual shape of the Intake Structure into account,” he adds. Throughout the contract, a series of 2”, 3” and 4” sump wells located around the perimeter of the excavaton were used to keep ground water low and prevent the excavaton fooding. Water pumped out of the wells was run into a series of three temporary setlement lagoons before being returned to the river.

Adopting the Groundforce solution helped BAM Civi l stay on programme and keep constructon costs down. “By making the excavaton follow the shape of the Intake Structure, we reduced the amount of material excavated by about 20%,” explains Mr McFadden.

“That not only saved tme but also reduced the amount of vehicle and plant movements involved while cutng the amount of material that had to be disposed of around the site.”

The excavaton took two weeks to complete and was back-flled afer completon of the Intake Structure 12 weeks later. The overall project is scheduled for completon in March 2013.

Project Factfile SROWLAND WATER TREATMENT PLANT

Construction of a new water treatment plant including intake structure, storage reservoirs and pumping mains. The new treatment plant form part of the Barrow Abstraction Scheme to provide potable water to County Kildare and the Greater Dublin Region.

• Employer: Kildare County Council • Locaton: Athy, Co. Kildare • Value: €22 million

• Commencement date: June 2011 • Completon: March 2013

Page 16 Contractors World - UK & Ireland Vol 1 No 7

Work in fnal stages, with the Groundforce frames in place.

 

           More information: Groundforce Email

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