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A23 Coulsdon Town Centre Improvement Scheme

Client: Transport for London

Contractors Designers: Scott Wilson, Tony Gee and Partners

Form of Contract: ICE 7th Edition

Dates work carried out: 2004 - 2006

Value: £38,000,000

The 1.73km road to bypass the centre of Coulsdon, a small Surrey town on the fringe of South London, was opened in December 2006 and is expected to reduce traffic volumes through the town centre by 80%.

Embracing innovation and value engineering HOCHTIEF redesigned one steel-composite bridge over the existing A23 from three to two spans, with reduced pile diameters, giving the potential to reduce costly service diversions.

A major rail interface with construction parallel to and 3 metres from the main London/ Brighton line required coordination with Network Rail for design and build of footbridges, piled retaining walls and a jacked box under the operational railway. Long-term traffic management on the A23 into London was maintained throughout.

Environmental and ecological control was essential, the route cutting through both SSSI chalk downland, a contaminated industrial site once used for rail sidings and a water “Source Protection Zone” (SPZ) together with mproximity to residential areas.

A key element was design and build of a jacked box tunnel to take the road under Smitham Junction station and railway, whilst it remained open. Working 24-hours a day 7 days a week this was completed on schedule within the planned 4-week programme, on 27th April 2006.

The heavily reinforced 8,500-tonne, 10m high 25m wide structure, with1.4m thick walls was moved 35m from its construction position. Through a combined mining and jacking operation over 12,000 tonnes of chalk was removed. Using up to 14,500 tonnes of hydraulic force the jacking, divided into three pushes each taking around eight days, averaged 400mm per hour. Apart from two breaks at eight-day intervals to reset the jacks and cast new jacking beams this continued 24-hours a day for 29 days.

The box was positioned accurately within design tolerance allowing the road to pass underneath the station. During the entire operation the Branch line and station remained fully operational, and not a single “train minute” was lost due to the works.