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Piling Out of danger

Foundations - Value engineering has saved 40% on a potentially tricky piling job in east London, reports Ruby Kitching.

Ground engineering catastrophes can come back to haunt following projects many years after they occurred.

Piles for a Telford Homes development near Island Gardens Docklands Light Railway (DLR) Station, east London, are just 3m from the site of a blow-out during tunnelling of the DLR Thames tunnel in 1998 after compressed air being used to counteract water pressure escaped. DLR expressed concern that the fully loaded piles could distort the tunnel lining, pushing it within the kinematic envelope of passing trains.

Ground is sandy gravel, and initially it looked as if contractor Westpile would have to sleeve 60 piles so that they would not load ground adjacent to the tunnel.

Combined with the cost of lengthening the piles in the danger zone to achieve required friction this would have cost £200,000. Instead, Westpile general manager Julian Gatwood spent £12,000 - a tenth of the final cost of piling - on a study to see whether, in practice, the tunnel would distort.

'We had a detailed survey done to confirm the tunnel profile and verify that perhaps the tunnel would not distort in the long term, ' says Gatwood.

The study revealed that sleeved piles would not be required, allowing 300 continuous flight auger piles of 350mm and 450mm diameter to depths of between 11m and 17.5m to be been installed last month. 'The result is Telford Homes can spend more money on the bathroom suites in the flats, ' he jokes.

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