Tunnel Vision

01 May 2008

Two rail tunnels in the uk have been reopened after completion of a 12 month refurbishment contract, worth UK£ 18 million (€ 26 million), by a partnership of Halcrow and Costain. Lining of tunnels in north Kent has been fast tracked through use of Cifa hydraulic slipform shutters and self levelling, self compacting concrete by tunnel refurbishment specialist Amalgamated Construction (Amco).

The Higham and Strood tunnels are 1,4 km and 2,1 km long, respectively, and were originally bored through chalk to carry a canal but were later converted for rail. Some sections of the tunnel were lined with brick but the unlined sections had suffered a series of rock falls, which forced Network Rail to restrict line speeds before closing the tunnel for refurbishment.

Working from the rails, raked piles and capping beams were installed to support a series of colliery arches, which in turn would provide support for a new cast in-situ concrete lining. The Cifa shutters, capable of lining up to 10 m of the tunnel in one go, were then rolled into position and up to 70 m3 of concrete was pumped into the shutters by rail for each pour.

Amco's team worked 24 hours a day during the week and put in 12 hour shifts at weekends to complete up to 60 m of tunnel lining each week. New drainage, cabling, track and signalling was also installed in the tunnel during the contract and completion means that the line speed through the tunnel has now been restored.

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