HS2 relaunches TBM for second bore

The 125m-long TBM named Dorothy will now dig the second tunnel under Long Itchington Wood in Warwickshire. It was initially launched in December 2021 and completed the first tunnel drive – and the first on HS2 – in July.

The second bore is due to be completed in summer 2023.

Over the four months since the breakthrough, the TBM’s gantries, which weigh over 1,000 tonnes, were taken back through the tunnel and reassembled at the north portal. The 10m-diameter cutterhead, weighing 160 tonnes, was moved by road in September. The TBM's 130-tonne tail skin and eight other large pieces from the TBM’s front shield and middle shield were also transported by specialist equipment.

This is the sixth tunnel launch on the project, but the first time a TBM has been reassembled and reused. Four other TBMs are currently in the ground, digging twin-bore tunnels under the Chilterns and London. When the TBM breaks through next summer, Long Itchington Wood Tunnel will be the first twin tunnel to be completed on HS2.

BBV tunnels delivery director Neil Johnson said it had been “an intense four months for the 300-strong team, including an intricate logistical operation to safely transport the TBM’s giant cutterhead and tail skin back to the north portal”.

Excavation of the twin-bore tunnel will produce around 500,000 tonnes of mudstone and soil. The spoil is being processed at an on-site slurry treatment plant and separated out before being transported by a 254m conveyer to be used to build embankments along the railway.