BRITAIN’s Deputy Prime Minister John Prescott was the principal guest at a holing-through ceremony in the 3·2 km North Downs Tunnel on the 74 km Section 1 of the Channel Tunnel Rail Link on June 7. Railtrack Chief Executive Gerald Corbett also attended.
Speaking before a roadheader broke through the final 800mm of chalk, Alan Myers, Contract Manager for CTRL project manager Rail Link Engineering, told 500 guests assembled 1·5 km from the country portal that tunnelling rates had reached 14m a day, with up to 80m cut in a week.
The tunnel has been built using NATM techniques, and a 2mm waterproof membrane will now be installed before the 350mm inner lining of unreinforced concrete is completed. This will give an internal diameter of 12·8m for the double track 300 km/h alignment.
The inner lining will include polypropylene fibres that would melt in the event of a fire, providing space for the concrete to expand and so prevent spalling, as happened in the Channel Tunnel fire in November 1996.
Myers said that the cost of the tunnel was £5m below budget and work was two months ahead of schedule. Union Railways stated that Section 1 is now ’one-third complete’. A statement from UR noted that Railtrack is currently undertaking due diligence for Section 2 ’with a view to exercising the option’. Opening of Section 2 is not envisaged until 2007.