AARSLEFF PILING is working on the transformation of a former London Underground site in Watford, Hertfordshire into more than 350 one- and two-bedroom apartments and three-storey town houses.
The Cassio Metro development is Linden Homes Chiltern's biggest design and build brownfield regeneration.
Aarsleff is using three selferecting fixed leader hydraulic drop hammer rigs to install 1,494 fully reinforced 250mm and 300mm square section precast concrete foundation piles.
The £607,000 contract works out at about 25,000 l/m of driven piling. Pile lengths are between 14m and 22m and are being driven through about 5m of overburden and made ground into the underlying chalk.
Aarsleff is pre-augering about 100 pile locations to loosen obstructions in the made ground before pitching and driving with a drop hammer.
About two-thirds of the piles need safe working loads from 250kN to 750kN. The remainder had to support 1,050kN and Linden had initially planned to use bored piling. Aarsleff suggested substituting this technique with its faster precast piled alternative and after three test piles. Linden opted for Aarsleff's solution.
The project is due for completion in 2007.