HS2’s TBM ‘Dorothy’ sets off for second tunnel bore under Long Itchington Wood

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2000 tonne tunnel boring machine ‘Dorothy’ sets off for the second tunnel drive under Long Itchington Wood in Warwickshire, making it the sixth tunnel launch for HS2.

HS2 Ltd’s 125 metre-long ‘Dorothy’ tunnel boring machine has launched for her second one-mile tunnel bore under Long Itchington Wood in Warwickshire, marking the next significant milestone for construction on the northern section of Phase One.

After launching in December 2021, the Balfour Beatty VINCI (BBV) tunnelling team worked around the clock in shifts over seven months, with the TBM becoming the first on the HS2 project to complete a tunnel drive in July 2022.

“After celebrating HS2’s first historic tunnel breakthrough in July, this TBM reassembly and relaunch is another first for the HS2 project. One year after Dorothy launched for her first drive, she’s now set off for the second bore, and we look forward to seeing the next HS2 tunnel breakthrough in summer 2023,” says HS2’s Senior Project Manager for Long Itchington Wood Tunnel, Doug Barnett.

Over the last four months since the breakthrough, the tunnel boring machine’s gantries, which weigh over 1,000 tonnes, were brought back through the tunnel and reassembled at the north portal. The huge cutter head, weighing 160 tonnes and with a 10-metre diameter, was moved by road during an intricate night-time operation 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 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.

“This has 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. This is another fantastic milestone for BBV and a proud moment for our fantastic tunnelling team,” says Balfour Beatty VINCI Tunnels Delivery Director Neil Johnson. 

The tunnel, which preserves the ancient woodland above, forms a key element in how HS2 is managing environmental impacts through the design of the railway, protecting Britain’s precious wildlife habitats. Long Itchington Wood is classified as a Site of Special Scientific Interest (SSSI) with complex ecosystems that have taken hundreds of years to establish.

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

The TBM is named ‘Dorothy’ after Dorothy Hodgkin, who in 1964 became the first British woman to win the Nobel Prize in Chemistry.

Source: © High Speed Two Ltd 2022

Image source: © High Speed Two Ltd 2022

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