Tunnel Boring Machine ‘Dorothy’ Achieves Milestone Breakthrough in England

A milestone breakthrough of tunnel boring machine “Dorothy” was recently celebrated as the giant cutterhead broke through the wall of the Long Itchington Wood Tunnel south portal in Warwickshire (England). The general contractor on the project is Balfour Beatty VINCI.

Launched in November 2022, the 2,000 ton TBM has completed its one-mile second bore, making it the first complete twin-bore tunnel on the High Speed 2 project.

After completing the first bore of the tunnel in July 2022, the 125-meter-long TBM was dismantled and returned to the north portal where it was reassembled ready to start its second journey.

Members of the Balfour Beatty VINCI tunneling team were onsite to witness the moment the huge cutterhead broke through the reception box headwall. This marks the culmination of a three-year operation, from site setup and TBM assembly, the first TBM drive and breakthrough and now completing the second breakthrough.

The tunneling team has been working around the clock in shifts for four months to operate the TBM, which has put 791 concrete rings in place, with each ring made from eight two-meter-wide segments that each weigh up to eight tons.

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 with complex ecosystems that have taken hundreds of years to establish.

Excavation of the twin bore tunnel has produced around 500,000 tons of mudstone, which is being processed at an onsite slurry treatment plant. From there, it’s separated out before being transported by a 254-meter conveyer to be used to build embankments along the route of the railway, removing the equivalent of around 30,000 heavy goods vehicles 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 3.5-mile tunnel bore in early 2024, between Water Orton in Warwickshire and Washwood Heath in Birmingham.