How did they build the underwater tunnel for the eurostar?
The French started from their side & the UK started from theirs. We met in the middle and linked the two together. Several huge boring machines were used. Below are a couple of BBC links about the drill (on sale on ebay at one pont) and the story of the build – nothing technical I’m afraid. The 3rd link is a history of the attempts to complete the link!
Actually there are three tunnels under the Channel – 2 running tunnels for the trains, one in each direction, and the smaller service tunnel which normally runs between the train tunnels for emergency vehicles, evacuating passengers from trains, etc. The running tunnels are linked through two “crossover caverns” under the Channel, so trains can be switched from one running tunnel to the other if part of the tunnel or track is closed for maintenance. They built each of the tunnels using huge “tunnel boring machines” (TBMs) – they built huge pits just inland from the coast on both sides of the Channel and started TBMs boring under the sea, and other TBMs boring inland to create the proper tunnel portals we see today. It’s these TBMs which bored inland which you can sometimes see today. Because the TBMs automatically lined the tunnels they built with concrete sections as they moved through the ground, the tunnels are slightly smaller in diameter than the TBMs themselves, so they couldn’t
Very briefly: They had machines based on a design invented by Marc Isambard Brunel, the father of Isambard Kingdom Brunel, when he was supervising the construction of the Rotherhithe Tunnel under the Thames around 180 years ago. The tunnelling face and those working on it are protected by a massive steel shield, which slowly advances as the tunnel progresses, with each stage of the tunnel immediately behind it being lined with sections of reinforced concrete. The machine is also linked to a conveyor belt system for removing the waste. The English and French sides each had one of these machines borrowing inwards so as to meet in the middle: the French called theirs ‘Diplodocus’. As the tunnels reached further and further under the sea, temporary rail lines and roads were laid to supply the workers at the tunnelling face and carry away the waste. The tunnelling machines were kept on course by a laser which was aimed in the direction the tunnel was to go and could detect even the slightes
