Britain’s new high-speed railway, HS2, which is being developed to connect London and Birmingham has achieved a major construction milestone with the completion of the first section of the Bromford Tunnel linking Warwickshire and Birmingham.
The Bromford Tunnel is a 3.5-mile (5.8km) twin-bore tunnel connecting Water Orton in North Warwickshire to Washwood Heath in Birmingham. Two giant tunnel boring machines (TBMs) – named Mary Ann and Elizabeth – are being used to excavate the tunnel.
On May 9, 2025, the Mary Ann TBM broke through, marking the end of her mission to excavate the first bore, while the Elizabeth TBM advances through the second bore.
The 125-meter-long Mary Ann TBM began constructing the Bromford Tunnel in July 2023. During the 22-month-long mission, the team on board the 1,600-tonne machine worked at depths of up to 40 meters. They skillfully navigated the TBM under the Park Hall Nature Reserve, the M6 motorway, and the meandering River Tame, which they crossed four times, with a headspace as low as five meters.
Mary Ann excavated around one million tonnes of spoil during the tunnel drive. In line with HS2’s sustainability policy, the excavated earth is being reused to support construction of the nearby Delta Junction, a complex network of 13 viaducts that will enable high speed trains to travel between London, Interchange Station in Solihull and Birmingham Curzon Street Station. The excavated material is transported via dedicated haul roads to minimize the number of construction vehicles on public roads.
At peak production, the TBM advanced at around 30 meters per day. The crew worked in tandem to navigate the giant boring machine, ensuring the cutterhead sliced through the earth, whilst simultaneously reinforcing the excavated tunnel with concrete segments, each weighing up to seven tonnes.
The precision-designed segments were manufactured at Balfour Beatty Vinci’s pre-cast factory at Avonmouth near Bristol. The TBM lined the tunnel walls with 20,797 individual segments, making 2,971 concrete rings to form the tunnel.
A 450-strong team supported the civil engineering feat. Men and women working on behalf of HS2’s construction partner, Balfour Beatty Vinci (BBV), worked around the clock, for just under two years, to complete the first section of the tunnel. The second bore is expected to be completed later this year by the Elizabeth TBM. Following the excavation, teams will begin fitting out the tunnel with cross passages, concrete finishing works and base slabs, and emergency and maintenance walkways.
Mark Wild, CEO, HS2 Limited, said: “Today’s breakthrough is a significant milestone for the project and I’m immensely proud of the men and women who have worked day and night to bring Mary Ann and her crew home safely.”
The tunnel breakthrough – HS2’s first in Birmingham – is a significant milestone for the project, which will almost halve journey times between Britain’s two largest cities, whilst freeing up valuable track space on the heavily congested West Coast Main Line for more local, regional and freight services.
The Washwood Heath site, where Mary Ann broke through, will soon become the nerve center for HS2’s operations. Next to the tunnel portal, HS2’s Depot and Network Integrated Control Centre will be built. From this site, trains will be serviced and stored, and the real-time operation of the railway will be controlled.
Washwood Heath is one of three key HS2 sites in the West Midlands, alongside the two new stations that will be built in Birmingham and Solihull. Collectively, the three sites have become a magnet for property investors and developers, spearheading multibillion-pound redevelopment projects in the areas nearby, which is forecast to add $13.3 billion (£10 billion) to the region’s economy over the next 10 years.