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Heads down on Heathrow contract


EXCLUSION ZONES above and below ground are complicating piling on approach ramps for a road tunnel close to Heathrow Airport's two main runways.

Bachy Soletanche is installing piles for complex approach ramps for a road tunnel.

Planes take off and land every 45 seconds within 800m of both sides of the site where Bachy Soletanche is piling. Accuracy is equally important 20m below ground, to prevent secant piles entering the danger zone above London Underground tunnels that cross the runway complex.

Tension piles up to 40m deep are being built in the exclusion zone, which has a 20m height restriction. Rebar cages are being assembled in short lengths and spliced together on site.

'If our jib rigs or rebar cages stray too high they become aeroplanes on the airport flight controllers' radar screens, ' explained Bachy Soletanche project manager David Newby.

The Airside Road Tunnel project will provide direct passenger access between airport terminals and remote aircraft stands. It will also link to the recently approved fifth passenger terminal.

Contractor Morgan Vince Est will assemble an earth pressure balance tunnelling machine to drive the tunnel's twin 9m diameter tubes from the approach ramps in June.

The sides of the approach ramps are formed from 1300mm male and female secant piles driven to a depth of 24m. The piles are installed by a fleet of BG30 rotary and BG22 CFA rigs equipped with computers to control torque and depth. Piling for the 900m run of wall is now about half way.

Piling at one end of the tunnel is being carried out only metres from plane taxiways, and at the other end between the runways; both have near continuous traffic. Below ground traffic is also a challenge, as a crucial section of the secant wall must be embedded just above the Piccadilly tube line's tunnel crown exclusion zone.

Working for contractor Laing Management, Bachy Soletanche is BAA's permanent geotechnical framework contractor. This £5.1M piling operation is the first of many in the planned £20M of foundation work needed for Heathrow's new T5 terminal.

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