Each of the machines bored through the sandstone and shale under the city centre at an average advance rate of 167m per week. The sandstone tunnels house a six-segment rhomboid and trapezoidal lining. Each segment is 1.7m long, 260mm thick and weighs about 3.75t. The thickness is so the segments can tolerate the push of the TBMs thrust rams, for situations where the TBM is not just pushing off the grippers.
The contractor was John Holland-CPB-Ghella. The reference design was undertaken by WSP Parsons Brinkerhof, Aecom, Cox, Hassall. The detailed designers were Hochtief Engineering, Noma Consulting, Pells Sullivan Meynink, McMillan Jacobs, Arcadis BG&E.
For more information, please see the feature in Tunnels and Tunnelling International, January 2020, pp.20-27
