Crossrail: Tunnelling beneath London – BBC News

Our guide John, a man who also helped build the Channel Tunnel, took us past all the machines, beeping lorries, cherry pickers and men, away from the lights, down a dark tunnel which eventually just, erm, stops.

In a few weeks’ time, he said, a 1,000-tonne machine will crunch through that wall. I tried to picture it, inching towards us through the clay. Spooky.

Then when it arrives, they’ll put it on some rails, drag it to the other end of the site, and it will start gouging out the wall at the other end.

So you can picture it, they’ve actually used diggers and sprayed concrete mixed with steel fibres (known as Shotcrete) to hollow out most of the stations, and the tunnelling machines connect up all the holes.

The exceptions are Paddington, Canary Wharf and Woolwich stations, which are essentially massive concrete boxes sunk into the ground.