Dorothy makes HS2 tunnelling breakthrough

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A 2,000-tonne tunnel boring machine called ‘Dorothy’ has made the first tunnelling breakthrough on HS2, Europe’s largest infrastructure project.

'Dorothy' makes HS2 tunnel breakthrough
'Dorothy' makes HS2 tunnel breakthrough - Andrew Hendry / HS2

Named after Dorothy Hodgkin, the 1964 Nobel Prize in Chemistry winner, the TBM completed its one-mile dig under Long Itchington Wood in Warwickshire.

The 125m long TBM started its journey at the tunnel’s North Portal in December 2021 and broke through the wall of the reception box at the South Portal site on Friday 22 July. Over the course of seven months Dorothy and her crew installed 790 concrete rings, each made from eight two-metre-long segments.

In a statement, HS2 Ltd’s CEO Mark Thurston said: “This is a historic moment for the HS2 project, and I’d like to congratulate everyone involved in delivering it. The 400-strong team, including tunnelling engineers, TBM operators and the construction workers at both portal sites, have pulled out all the stops to achieve this fantastic milestone.

“This milestone demonstrates the significant momentum behind Britain’s new zero-carbon railway, creating thousands of jobs and apprenticeships, along with hundreds of opportunities for businesses right across the country, helping fuel our economic recovery.”

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

A 254m long conveyor at the north portal site takes the excavated material over the Grand Union Canal, removing the equivalent of around 30,000 HGVs from local roads.

HS2 Ltd said that 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 be reassembled for launch on the second bore of the tunnel.