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The Bromford tunnel is a high-speed railway tunnel under construction in North Warwickshire and Birmingham, England, and will serve to bring the High Speed 2 rail line into Birmingham upon completion.

The 5.6 km (3.5 miles) twin-bore tunnels will be situated between Water Orton and Washwood Heath.

History

The contract to build the tunnel, as part of the wider N1 and N2 lots on the HS2 programme, was awarded to the Balfour Beatty Vinci JV on 1 April 2020, valued at c.£5 billion. This followed them being named by HS2 as part of the intention to award in July 2017.

The route was initially envisioned in the High Speed Rail (London - West Midlands) Act 2017 to be a tunnel, 2.86 km (1.78 mi) long (in Work No. 3/203) and partly on viaduct, less than 30 m (98 ft), in length (in Work No. 3/157).

On 20 January 2022, HS2 Ltd made a Transport and Works Act Order application to remove the words "partly on viaduct" in the description of the works, in a bid to extend the tunnel by around 3 km (1.9 mi) instead. This decision was claimed to reduce land take, minimise impacts on the Park Hall Nature Reserve, avoid the need to redirect the River Tame, and reduce construction traffic.

The Secretary of State for Levelling Up, Housing and Communities and Secretary of State for Transport recovered an appeal to these plans, which had been declined by North Warwickshire Borough Council and had a subsequent appeal dismissed by an inspector of the Planning Inspectorate. It was granted Schedule 17 approval on 14 May 2024.

The two Herrenknecht tunnel boring machines (TBMs) used to construct the tunnel were named Mary Ann, after Mary Ann Evans (with the pen name, George Eliot) and Elizabeth, after Elizabeth Cadbury. Most of the second TBM to be delivered, Elizabeth, was repurposed from TBM Dorothy used to construct the Long Itchington Wood tunnel, with a new outer cutter-head and shield ordered.

Design

The tunnel passes underneath the Park Hall Nature Reserve, River Tame, and M6 motorway, and runs up to 40 m (131 ft) underground.

The tunnel will have 13 cross-passages, spaced every 500 m (1,640 ft), and 5.5 m (18.0 ft) wide.

The eastern portal at Water Orton will have a porous portal, likely in the form of a perforated concrete structure, to mitigate the sound and shockwave produced by the piston effect of moving trains, travelling 230 km/h (145 mph).

The decision the extend the tunnel to over 3 km resulted in the need for an intermediate shaft to allow for adequate airflow. The tunnel will have a 47 m (154 ft) deep, 18.6 m (61 ft) diameter ventilation shaft at Castle Vale, around the halfway point of the tunnel. The headhouse, located in the Castle Bromwich Business Park, will have pre-cast concrete walls with an overlaid "flexi-brick" lattice facade made of ceramic tiles and a 'green roof'.

Construction

Tunnelling and excavation is primarily through Mercia Mudstone, at mostly BGS grade II weathering. The groundwater level is, at most, 30 metres (98 ft) above the tunnels' roof.

The variable pressure TBMs used to construct the tunnel have a cutter-head diameter of 8.62 metres (28.3 ft), and weight approximately 1,600 tonnes each. They are both expected to take 16 months to complete the tunnel, employing around 450 people.

The TBM Mary Ann started boring in August 2023 from an underground box structure, measuring 160 m × 30 m × 15 m (525 ft × 98 ft × 49 ft), from the eastern portal at Water Orton towards the 22 m (72 ft) deep portal at Washwood Heath. This was followed by TBM Elizabeth in March 2024.

A total of 41,594 concrete segments, produced by the joint venture's pre-cast concrete factory in Avonmouth, Bristol, will be used to support the tunnels. These will form 5,942 rings, weighing 49 tonnes each. Forty percent of the cement used was replaced with ground granulated blast-furnace slag (GGBS), claimed to reduce the overall carbon footprint involved. The TBMs are expected to excavate 1.87 million tonnes of material, which will be treated by the on-site slurry treatment plant for use on HS2's delta junction, south of Water Orton.

Mary Ann is expected to break through by the end of 2024, while Elizabeth is expected to finish the drive by autumn 2025.

References

1. "Balfour Beatty - VINCI joint venture is awarded the contract for HS2's main civil engineering works packages lots N1 and N2 in the United Kingdom". Vinci SA. 15 April 2020.
2. "Balfour Beatty joint venture to be awarded HS2 contracts valued at c. £2.5 billion". Balfour Beatty. 17 July 2017. Retrieved 16 December 2024.
3. "High Speed Rail (London - West Midlands) Act 2017". www.legislation.gov.uk. Archived from the original on 26 November 2018.
4. ^ "Bromford Tunnel Transport and Works Act Order Application". HS2. 20 January 2022.
5. ^ "Bromford Tunnel". HS2.
6. Barber, Phil; Stewart, Paul (14 May 2024). "Appeal made by High Speed Two Limited (HS2 Ltd) against the decision of North Warwickshire Borough Council to decline to determine the request for the approval of plans and specifications made under Schedule 17, comprising the Water Orton cutting, including the Bromford tunnel east portal and Attleboro Lane overbridge and ancillary works" (PDF). GOV.UK.
7. "HS2 unveils huge tunnel boring machine ready to dig HS2's Bromford Tunnel in the West Midlands". HS2. 14 June 2023.
8. "The last HS2 tunnel boring machine in the West Midlands starts digging towards Birmingham". HS2. 5 March 2024.
9. Smart, Belinda (26 November 2024). "How UK and international tunnelling projects are reducing their environmental impacts". New Civil Engineer.
10. ^ "Balfour Beatty VINCI gets second giant HS2 tunnel boring machine ready to start digging". Balfour Beatty. 12 December 2023.
11. ^ Plisner, Peter (30 August 2024). "HS2 Bromford Tunnel reaches halfway mark". Rail.
12. ^ "High Speed 2 Contracts N1 & N2" (PDF). Gall Zeidler Consultants. Archived from the original (PDF) on 16 December 2024.
13. Cartwright, Mark (9 December 2024). "Bromford Tunnel extension - design and environmental benefits with no additional land take". HS2 Learning Legacy.
14. Thomas, Tris (28 August 2024). "HS2's Bromford Tunnel TBM reaches halfway". Tunnelling Journal.
15. "Building works associated with the construction of an intermediate shaft headhouse building serving the Bromford Tunnel along with associated lighting, security fencing, bollards and road vehicle parking". Birmingham City Council. 4 March 2023.
16. "Balfour Beatty VINCI unveils huge tunnel boring machine ready to dig HS2's Bromford Tunnel in the West Midlands". Balfour Beatty VINCI.
17. "HS2's "Elizabeth" Begins Digging Second Birmingham Tunnel". Rail Technology Magazine. 6 March 2024.
18. "HS2 completes first viaduct structures at Delta Junction". HS2 News and Information. 9 September 2024.

• High Speed 2
• Tunnels in Warwickshire
• Tunnels in Birmingham, West Midlands
• Railway tunnels in England
• Buildings and structures under construction in the United Kingdom
• Rail infrastructure under construction