A team has completed earthworks operation to construct the tunnel’s west portal. Credit: © Balfour Beatty.

Balfour Beatty Vinci has reached a milestone in the construction of the High Speed Two (HS2) gateway to Birmingham. 

The tunnel boring machine (TBM) ‘Mary Ann’ reached the halfway point in the excavation of the first bore of the Bromford Tunnel.  

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The TBM has excavated and constructed 1.75 miles of tunnel starting from Water Orton last year and is now progressing under Castle Vale. 

This 125 metre (m)-long ‘Mary Ann’ is operating approximately 40m underground, having already navigated beneath the Park Hall Nature Reserve and the River Tame.  

The machine is set to continue its journey adjacent to and beneath the M6, with a breakthrough at Washwood Heath expected early next year.  

A total of 20,797 concrete segments will be installed by ‘Mary Ann’, forming 2,971 rings to create the tunnel structure. 

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At Castle Vale, a 47m-deep ventilation shaft marks the midpoint of the TBM’s path.  

This shaft, with an 18.6m diameter, will incorporate cross passages linking the two tunnel bores for ventilation, servicing, and emergency access.  

A headhouse will crown the shaft, with the entire structure scheduled for completion in 2027. 

Meanwhile, ‘Elizabeth’, the second TBM for the project, commenced work on the tunnel’s second bore in March 2024 and is anticipated to conclude by the end of 2025.  

Together, the TBMs will extract approximately 1.87 million tonnes (t) of material. 

It is being processed at an on-site slurry treatment plant for reuse in the construction of a network of 13 viaducts at the Delta Junction. 

Balfour Beatty VINCI tunnelling director Jules Arlaud 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.” 

HS2 has constructed dedicated roads, including an access from the M6/M42 link roads, to facilitate the movement of construction materials and reduce the impact on public roadways.  

In anticipation of the TBMs’ arrival at Washwood Heath, earthworks operation to construct the tunnel’s west portal has been completed. 

The west portal forms the beginning of a 750m-long cut and cover structure, which is currently under excavation and construction.  

Earlier in August 2024, Balfour Beatty Vinci installed a 1,600t bridge over the Birmingham to Derby railway line in Saltley.