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Story of the job

SITE REPORT

THE £33 million Coulsdon Relief Road was first proposed more than 30 years ago and the longsuffering folk of Coulsdon will be celebrating this October when the scheme is finally due to open.

When completed the 1.73 km road is expected to reduce the traffic running through the town centre by 80 per cent.

The scheme is to build a new road alignment of the A23 to bypass the town centre of Coulsdon, a small Su r rey town on the edge of Greater London.

Hochtief was awarded the contract in late 2003 from a shortlist of six contractors, having submitted a tender proposal in 2002 working with Scott Wilson Rail.

The 37 m long concrete tunnel box, to which a mining shield was then stitched, took eight months to build.

The tunnel box was heavily reinforced with steel to ensure against cracking. It is designed to be a water retaining structure even though the water table is 10 m below ground. This ensures the concrete will not crack or stain in contact with water.

The approach to the tunnel called for major excavation of earth and the deep cutting is stabilised by contiguous bore-piled retaining walls.

Crossing the railway line the relief road drops down underneath Smithan Station to join the A23 at the northern end.

This called for an 8,500 tonne tunnel box 37 m long, 25 m wide and 10 m deep tunnel underneath the railway lined with 1.4 m thick concrete.

The tunnel is wider than or iginally planned when the scheme was in the hands of the Highways Agency because a pedestrian subway with cycle lane has been added.

The carriageway consists of a single-lane southbound carriageway and two northbound carriageways that include a priority lane for public transport, HGVs and motorcyclists in line with the London mayor's transport strategy.

Under the contract, Hochtief has also built a new footbridge over the railway line to replace the subway that had to make way for the road tunnel.