The 1,600 tonne, 8.62m diameter Herrenknecht TBM, ‘Mary Ann’ digging the first bore of HS2’s 5.6km long Bromford Tunnel – the project’s gateway to Birmingham – has reached the halfway point.
Mary Ann has excavated and built 2.8km of the first bore of the tunnel since it started digging from a large underground box in Water Orton last year.
Driving around 40m underground towards Washwood Heath in Birmingham, the TBM has excavated under the Park Hall Nature Reserve and River Tame and is now passing under Castle Vale. It will continue adjacent to and under the M6 before breaking through at Washwood Heath early next year.
A total of 20,797 concrete segments will be put in place by the machine, making 2,971 concrete rings to form the tunnel.
The tunnel’s 47m deep ventilation shaft at Castle Vale marks the halfway point of the TBM. The shaft, which is 18.6m in diameter, will feature cross passages which will eventually link to the two tunnels either side to provide ventilation, servicing and emergency access. A ‘headhouse’ will be built on top of the shaft, and the whole structure will be complete in 2027.
‘Elizabeth’, the second TBM started building the tunnel’s second bore in March 2024 and is due to finish her journey towards the end of 2025.
The two TBMs will remove 1.87M tonnes of excavated material, which is being sifted at the on-site slurry treatment plant and reused on nearby sites at the Delta Junction, where a complex network of 13 viaducts is being built. HS2 has built dedicated roads between these construction sites, including an access off the M6/M42 link roads, in order to take lorries off public roads.
In preparation for the arrival of the TBMs at Washwood Heath, a huge earthworks operation has been completed by a team of 130 people to build the tunnel’s west portal, which at 22m below ground is the deepest of the four tunnel portals on the Midlands section of the HS2 route.
The portal is at the start of a 750m long cut and cover structure, which is currently being excavated and built. This is where HS2 trains will emerge from the Bromford Tunnel and travel below ground level, before raising up onto a series of viaducts through Birmingham’s industrial heartland and into Curzon Street Station.
Jules Arlaud, Tunnelling Director for the contractor Balfour Beatty VINCI said, “Reaching the halfway point on this complex stretch of the HS2 route into Birmingham is a great milestone for our 180-strong tunnelling team. We’re looking ahead now to delivering the final stages of tunnelling, and celebrating the breakthrough of both TBMs at Washwood Heath next year.”
Rosa Diez, Tunnels Technical Lead for Mott MacDonald/Systra Design JV said, “We are incredibly proud of the work we have accomplished as a highly collaborative team in reaching the halfway point at Bromford Tunnel. Achieving such a tunnelling milestone of this diameter and in challenging ground conditions under Birmingham is an engineering feat which the experienced team has embraced.
“Mary Ann and Elizabeth will complete their tunnelling journey into Birmingham leaving a long-lasting legacy of engineering achievement and progress for the region.”
The specialist tunnelling teams are from UK firm Tunnelcraft, and Solihull-based Rorcon, with a total of ten apprentices including formerly unemployed people from the local area who now have jobs on the project.
Once complete, HS2 services will run between London and the West Midlands on a dedicated high-speed line before linking reaching destinations further north via the existing West Coast Main Line. It will provide significantly more efficient and faster journeys, while relieving pressure on the most congested southern end of the West Coast Main Line, allowing more local and freight trains to operate.
Herrenknecht
Pioneering Underground Technologies - Herrenknecht AG is the technology and market leader in mechanized tunnelling. As the only company worldwide, Herrenknecht delivers cutting-edge tunnel boring machines for all ground conditions and in all diameters - ranging from 0.10 to 19 meters.
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