The UK’s HS2 tunnelling team of Balfour Beatty/VINCI (BBV JV) has celebrated the milestone breakthrough of its 10m diameter Herrenknecht TBM ‘Dorothy’ at the Long Itchington Wood Tunnel south portal.
Launched in November last year, it’s only taken four months for TBM to complete its 1.6km second bore, making this the first complete twin-bore tunnel on the HS2 project.
After completing the first bore of the tunnel in July 2022, the machine was dismantled and returned to the north portal where it was reassembled ready to start its second journey.
Members of the BBV JV were on site to witness the dramatic moment when the cutterhead broke through the reception box headwall. This marks the culmination of a three-year operation, from site set-up and TBM assembly, the first TBM drive and breakthrough, and now completing the second breakthrough.
Michael Dyke, Chief Executive Officer for Balfour Beatty HS2 Major Projects, added:
“Successfully completing the first twin-bore tunnel on Britain’s new, highspeed railway is yet another demonstration of how works continue to progress at pace across the project. It’s a huge achievement, not only for Balfour Beatty VINCI, but for everyone connected with HS2.
“Watching Dorothy break through her second one-mile journey today was only possible thanks to months of hard work and dedication from our 400-strong project team, who deserve a special mention for safely delivering this incredible feat of engineering.”
Tunnel Surveyor Apprentice Jake Flood from Walsall, who joined Balfour Beatty VINCI’s tunnelling team last year was on site to mark the launch of the TBM back in November. Celebrating with the team at the breakthrough today, he said:
“I witnessed the launch of Dorothy just after I started my apprenticeship last year. It was an incredible moment, and I am thankful that I have had the opportunity to support the tunnelling team over the past four months.
“It’s very special to be invited to watch the breakthrough alongside my colleagues. Working on a project with such huge feats of engineering really is a once-in-a-lifetime opportunity and I can’t think of a better way to start my career.”
The tunnelling team have been working around the clock in shifts for four months to operate the TBM, which has placed 791 concrete rings in place, with each ring made from eight 2m wide segments each weighing up to 8 tonnes.
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 has produced around 500,000 tonnes of mudstone, which is being processed at an on-site slurry treatment plant. From there, it is separated out before being transported by a 254m conveyer to be used to build embankments along the route of the railway, removing the equivalent of around 30,000 HGVs from local roads, reducing impacts on the local community and cutting carbon.
Over the next few weeks, work will begin to dismantle the shield from the TBM, while the rest of the machine will be pulled back to the start of the tunnel and disassembled, ready for transportation to East Birmingham. There, the TBM will be fitted with a new shield so that it can begin a 5.6km tunnel bore in early 2024, between Water Orton in Warwickshire and Washwood Heath in Birmingham.