BRITAIN’s HS2 Ltd is today (July 26) celebrating the first tunnelling breakthrough on what is claimed to be Europe’s largest infrastructure project: the construction of a new high-speed line linking London with Birmingham and Lichfield.

A 2000-tonne TBM named ‘Dorothy’ – after Dorothy Hodgkin, who in 1964 became the first British woman to win the Nobel Prize in Chemistry – has completed its 1.6km dig under Long Itchington Wood in Warwickshire.

The 125m-long TBM, which started its journey at the tunnel’s North Portal in December 2021, broke through the wall of the reception box at the South Portal site on July 22. For the nearly 400 people working for HS2’s main civil engineering contractor, Balfour Beatty Vinci (BBV JV), this is an important milestone on the HS2 project.

The tunnelling team have been working around the clock in shifts for seven months to operate the TBM, which has installed 790 concrete rings, with each ring formed from eight 2m-long segments. The tunnel will help to preserve the ancient woodland above it, which is classified as a Site of Special Scientific Interest (SSSI).

While constructing both bores of the tunnel, the machine is removing around 250,000m3 of mudstone and soil, which is being transported to an on-site slurry treatment plant. There the material is separated out before being reused on embankments and landscaping along the route.

A 254m-long conveyor at the north portal site, which takes the excavated material over the Grand Union Canal, removes the equivalent of around 30,000 HGVs from local roads, helping to reduce the impact of the construction project on the local community and cutting carbon emissions.

Over the next four months, the cutterhead and front section of the TBM will be dismantled and transferred back to the north portal, while the bulk of the machine will be brought back through the tunnel. It will then be reassembled, ready for construction of the second bore of the tunnel.