2003•Proceedings of the Institution of Civil Engineers - Civil EngineeringRequires access
Channel Tunnel Rail Link section 1: North Downs tunnel
Paul Watson
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Abstract
The 3·2 km tunnel under the North Downs in Kent is the longest tunnel on the first section of the £5·2 billion Channel Tunnel Rail Link. It is also has the largest cross-section of any rail tunnel in Europe since no pressure relief shafts were allowed in the environmentally protected area above. This paper reports on how a value engineering process led to a significant change to the tender design, resulting in a 15% saving in cost and programme. Extensive tests of the overlying chalk showed it was stiffer than predicted, thus permitting the use of a thinner unreinforced secondary lining and a flat invert.