HS2 Birmingham tunnel excavation reached halfway point during its journey to build the 5.6 km Bromford Tunnel. The 1,600 tonne tunnel boring machine (TBM), named ‘Mary Ann’ has excavated and built 2.8 km of the first bore of the tunnel since it started digging from a large underground box in Water Orton last year.
Driving around 40 metres 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 47-metre-deep ventilation shaft at Castle Vale marks the halfway point of the TBM. The shaft, which is 18.6 metres 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 second bore of HS2 Birmingham tunnel in March 2024 and is due to finish her journey towards the end of 2025.
The two TBMs will remove 1.87 million 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 22 metres 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 750-metre-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.
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