PLANNING THE TUNNELS FOR THE HIGH-SPEED RAIL LINK

This article, based on a presentation to the Institution of Civil Engineers on 21 October 1994, relates the complicated history of the proposed high-speed rail link from the Channel Tunnel to London. The new link is required for commuter traffic between Essex and London as well as for Channel Tunnel traffic and freight. The two alternatives considered for the 110km link are the Southern and Eastern Approaches. The additional cost of meeting all objections by local communities, by building 18 more tunnels, would cost an additional 2 billion pounds. The design criteria for tunnels along the route allowed for alignment, cross section, safety, surface impact, and environmental issues. Safety considerations included: (1) tunnel configurations; (2) location and frequency of cross passages; (3) numbers and locations of emergency access shafts; (4) ventilation and smoke control; (5) provision of walkways; (6) provision of suitable mechanical and electrical equipment. Tunnels outside London will include: (1) bored twin tunnels under the River Thames (immersed tubes and a bridge were also considered); (2) the 810m long Pepper Hill tunnel; (3) the 3km long tunnel under Blue Bell Hill; (4) the 1050m long Ashford tunnel. Inside London, the two alternative routes from St. Pancras and Kings Cross would have 16.5km and 14km of tunnels, respectively.