CTRL tunnel milestone

The tunnel currently being built under the river Thames in London, as part of the Channel Tunnel Rail Link (CTRL), reached the 1km point this week.

Tony Bermingham, contract manager for RLE, said: "Progress has been good and the TBM is now performing well will the conditions it is meeting in the ground. We are within our programme to create the first tunnel dug under the Thames, adjacent to the Dartford Crossing, for over two decades."

The 8.16m diameter full-face slurry Herrenknecht TBM set off in July from Swanscombe in North Kent towards Purfleet in Essex on a 2.5km drive, which should take about eight months.

The Hochtief/Murphy JV is operating the machine that will slice through alluvium, terrace gravels and chalk, placing 33,000 concrete rings as it goes. The fully pressurised head is designed to withstand the 4.5 bar expected at the maximum 40m tunnelling depth.

When complete in 2007, the US$8.1bn CTRL will halve journey times from central London to the Channel Tunnel.