WALES'S NEW National Swimming Pool in Swansea proved a challenging project for UK foundation contractor Aarsleff Piling.
Aarsleff expected to drive nearly 560 of its 300mm square, 11-18m long, single and jointed precast piles through about 6m of fill and dense gravel for the Olympic-size pool.
This had to be reassessed when stiff fill and obstructions made driving difficult.
'We always knew it would be quite hard driving and expected problems with a few piles hitting obstructions, ' said Aarsleff Piling contracts engineer Gary Kime.
'We needed an alternative solution and suggested driving replacement steel tubes next to the affected concrete piles and in particular trouble spots.We can put the same impact energy from the drop hammer into a much smaller area of steel and believed that with this method we could get through the very stiff fill and deal with the obstructions.'
For the replacement steel tubular piles Aarsleff used 244.5mm outside diameter oil well casing, which was collared and coupled together in 10-13m long sections.The precast concrete and tubular steel piles, driven on an approximate 3m grid pattern, were designed for working loads of up to 650kN. Testing firm Precision Monitoring and Control carried out the dynamic and static testing to verify capacity of the concrete piles and replacement steel tubes.
Frank Lambert, site manager for main contractor Shepherd Construction, said: 'We anticipated hitting problems and predicted about 10% of the precast concrete piles might hit obstructions and break, but in the end only about 7% were affected.'
Shepherd, working for client City and County of Swansea, is building the 50m by 25m practice pool at Swansea University's sports centre.Work began on the £9.8M contract in March 2001 and is due to be complete by October 2002. Aarsleff 's piling contract is worth £245,000.