The Channel Tunnel
The Engineer posted on October 17, 2006 |

Trains enter the tunnels at terminals located at Folkestone in the county of Kent in South-East England and at Calais in the Nord-Pas-de-Calais region of France.

The tunnels contain a railway system, which takes shuttle trains between the terminals at Folkestone and Calais LE SHUTTLE and through-trains which link with the national rail networks of France and Great Britain.

Eurotunnel is the company, which owns and operates the Channel Tunnel and its railway system.

Construction

The tunnels are 50 kilometers long and 30 meters apart and were bored in the rock strata under the Channel at an average depth of 45 meters below the seabed.

The two large tunnels (7.6 meters diameter) each contain a single-track railway line.

The smaller service tunnel (4.8 meters diameter) is located between the two rail tunnels and is equipped with a wire guidance system for specially designed service tunnel vehicles.

All three tunnels are connected every 375 meters by a cross-passage, which gives access to the service tunnel in case of emergency. The cross-passages are also used for ventilation and maintenance service access.

Every 200 meters, the two rail tunnels are linked by piston relief ducts. These are used for the regulation of the air pressure in the tunnels.

All three tunnels are lined with concrete linings.

Geology & Surveying

UK FRANCE Shakespeare Cliff / Sangatte

Undersea crossovers / rock strata - chalk / chalk marl / gault clay depth beneath seabed - average 25 -45 meters

Satellite data from geophysical surveys provided information about the geology and helped to determine the alignment and route of the tunnel.

To maximize the favourable ground conditions, the tunnels were excavated in the layer of chalk marl except for a 3-kilometer section on the French side.

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