Having first bored through a 19m-high reinforced-concrete headwall, the 9.92m-diameter Herrenknecht variable density TBM began its journey to bore the 1.6km tunnel under Long Itchington Wood in Warwickshire, England.

Around 170 engineers have worked on the 2,000t, 125m-long machine (‘Dorothy’) during its onsite construction and assembly. Teams from contracting JV Balfour Beatty Vinci (BBV) will now work shifts around the clock to operate the machine for around five months as it excavates the first bore of the tunnel – which will also be the first to be completed on the HS2 project.

After the machine breaks through at the south portal in spring 2022, it will be disassembled and taken back to the north portal to excavate the second bore which is due for completion in early 2023.

TBM excavation will remove 250,000m3 of mudstone and soil which will be conveyed to the on-site slurry treatment plant where the material is separated out before being reused on embankments and landscaping along the route.

The tunnel will preserve the ancient woodland above – a Site of Special Scientific Interest (SSSI) – which has complex ecosystems that have taken centuries to become established. The final section at the south end of the tunnel will be a ‘green tunnel’ – a ‘cut and cover’ that will have a soil roof to integrate the portal into the natural landscape. These approaches, says HS2 Ltd, are key elements in how it is managing environmental impacts through the design of the railway, thereby preserving Britain’s precious wildlife habitats.

“Today is another major milestone for HS2. You can see the real progress the project is making as we launch this TBM on one of HS2’s largest sites in the Midlands, contributing to massive job creation in the region,” said HS2 CEO Mark Thurston.

“More than 20,000 jobs and over 650 apprenticeships are already being supported by HS2, which is set to transform transport links between Britain’s major cities, free-up space on the rail network for more freight and local services, and support the UK’s transition to net zero carbon emissions.”

A total of 10 TBMs will work on Phase One of HS2, excavating 102km of tunnel between London and the West Midlands.