A SERIES OF heavy-duty, hydraulically-operated tubular struts was critically needed to support a 60m long retaining wall at the £45M City of Edinburgh Council's new headquarters.
Being near the city's Waverley Station and within 8m of the main Edinburgh-London railway line, the excavation is well within the designated rail support zone.
Carey Group engineering manager Andrew Richards, says: 'As the wall is so close to the main railway line, the results of failure or excessive deformation were so horrendous as to be beyond contemplation.
'It was crucial for us all to get it exactly right. This meant it was essential to provide shoring with a system that would minimise inward deflection of the piles to reduce the risk of any significant settlement within the heavily rail-tracked area.' Groundforce Shorco (GS) won a contract worth more than £24,000 to provide the 80t capacity struts used to prop up the 8m high, 600mm diameter contiguous pile retaining wall, which was positioned at the northern boundary of the development.
'We were pleased with Groundforce Shorco's technical advice and input to the scheme, ' says Richards.
The propping was designed inhouse by civil engineers Carey Group, with some technical assistance from GS, a division of plant equipment hire company Vp.
The solution meant installing 11.6m long tubular struts at approximately 6m centres, raking between a high-capacity waling beam of twin universal sections about 12m long and substantial mass-concrete thrust blocks founded on rock. The waling beams take a horizontal force of 11.5t/m.
The main contractor for the development, which is due for completion in September 2006, is Miller Construction.