Crossrail tunnellers make final breakthrough

In the last of a number of celebrated tunneling “breakthroughs” (there have been eighteen in total) the project’s final TBM  - Victoria - broke through into Farringdon station, marking the end of a painstaking process that began almost three years ago.

During this process eight 1,000 tonne, £10m machines have excavated and built 26 miles of brand new 6.2m diameter rail tunnels under London.

The majority of the machines used to create the network are so-called earth pressure balance machines (EPB), which vary both their advance rate through the ground and the rate at which they extract waste in order to maintain a pressure on the cutting face and prevent tunnel collapse.

As these machines move through the ground precast concrete segments are ferried to the front of the machine, grabbed by giant hydraulic arms, and put in place to form the lining of the tunnel. The machine propels itself through the ground using hydraulic rams that push against the edge of the last ring built.