A RECENTLY completed foundation contract in London's Mayfair had to meet strict environmental criteria.
The site is opposite the prestigious offices of Grosvenor Estates and behind the exclusive Claridges Hotel, home to celebrity chef Gordon Ramsey.
Grimsby-based foundation contractor Expanded Piling also had to deal with buried foundations before piling for the new office and retail scheme could start.
'The biggest problem was the concrete in the ground, ' said Expanded Piling site foreman Gary Brown. 'The existing piles may not have been exactly where they were meant to be, so it was fingers crossed that we didn't hit any on the way down.'
Initially it was planned to core through the obstructions using a 860mm diameter corer. 'But because the concrete was so hard, coring all the positions was taking too long, so to pull back some time, some of the pile caps were broken out, ' Brown said.
The 'very, very hard' concrete was broken out at 60 of the 90 pile positions - but only at certain times of the day, to minimise disruption. Breaking out was only allowed from 8am-10am, 12pm-2pm and 4pm-6pm.
Expanded's £300,000 contract was for client Grosvenor Estates and Hammerson joint venture partnership. The main contractor is Carillion and Clarke Nicholls and Marcel is engineer.
Site geology comprises 2m of fill overlying London Clay to about 32m with the clays and sands of the Lambeth Group beneath.
Bored piling was carried out in February, with Expanded installing about five piles a day. Piles were temporarily cased down to about 6.5m, through the fill and the upper horizon of soft weathered London Clay.
Most were 600mm diameter, although some were 750mm. Ranging between 38m and 42m long, the piles were installed using a Watson rig on an Ajax C60 base and were designed by Expanded to support loads of between 1450kN and 2450kN.
The new building, designed by architect Rolfe Judd, replaces a demolished 1960s structure.When completed in autumn 2003, it will provide about 5000m 2of space, with six floors of offices and three new retail units fronting Grosvenor Street or Brooks Mews to the rear.