HS2’s Second Giant Tunnel Boring Machine Assembled and Set to Start Digging Into Birmingham

HS2’s Second Giant Tunnel Boring Machine Assembled and Set to Start Digging Into Birmingham

The UK’s High Speed 2 (HS2) rail network took a significant step forward this week as specialists assembled a 1,600-tonne tunnel boring machine (TBM) set to begin excavating the second bore of the Bromford Tunnel into central Birmingham next spring.

The behemoth machine joins ‘Mary Ann’, the first TBM already a third of a mile into digging the tunnel’s first bore since its launch in August 2022. Once the newly assembled TBM receives a name and initiates drilling operations, HS2 will have two giants burrowing on a 24/7 basis to complete the project’s 3.5-mile route under North Warwickshire and into Birmingham’s Washwood Heath.

While future legs of High Speed 2 have faced recent uncertainty and proposed cutbacks to their scope, construction on the project’s initial core links continues advancing at high speed.

This milestone underscores recent construction momentum for HS2, with over 9,750 workers building infrastructure along the route. “We’re now at peak construction, with people working hard across all of our sites to realise the promise of high speed rail in the UK,” said HS2’s Senior Project Manager Catherine Loveridge.

Most of the new machine has been reused from the TBM ‘Dorothy’ that completed the Long Itchington Wood Tunnel excavation in Warwickshire earlier this year. HS2 Project Manager Loveridge explained, “Over the last few months, Dorothy’s disassembled sections have been transported here for reassembly, with the addition of a newly manufactured smaller diameter cutter head and shield specifically sized for the Bromford Tunnel route.”

The TBM will be a 90-person team working around the clock under HS2’s principal contractor, Balfour Beatty VINCI (BBV) and specialist tunnelling subcontractor Tunnelcraft. BBV’s Tunnelling Director Jules Arlaud said, “Getting to this stage has required extensive planning and coordination between our partners, but we are eager to test and launch this machine next Spring.”

The mammoth undertaking will see each TBM remove nearly 1 million tonnes of excavated spoil as they drive their respective bores over the 16-month-long digging operation. The material will be transported back for sifting and reuse at nearby HS2 construction sites.

Producing the tunnel will require over 40,000 specially designed concrete segments to form its walls as the TBMs move forward. The segments are fabricated at BBV’s Avonmouth factory using high-strength concrete with reduced cement content and emissions. “We’ve applied precision 3D scanning techniques to guarantee dimensional accuracy in manufacturing the segments critical to achieving HS2’s high safety and reliability standards,” Arlaud added.

Rosa Diez, lead tunnel designer for BBV consultants MMSDJV, stated that the project’s extensive sensor instrumentation will enable continuous condition monitoring. “Data gathered from Mary Ann’s progress has already helped optimise programming for the second TBM regarding power, face pressure, and other parameters – that learning will continue as we bring our second giant online next year.”

With peak construction now underway across the route, HS2 continues working toward its target operations launch date range of 2029 to 2033. The new infrastructure significantly increases rail capacity in the UK, promotes redevelopment of areas around stations, and meets sustainability goals through zero direct emissions trains and expansive tree planting programs.

Loveridge summed up the milestone of the second Bromford Tunnel boring machine coming online: “Seeing this assembly completed to plan keeps momentum going for delivering cleaner, faster, and more reliable high speed rail to Britain’s future.”


  • Specialists complete the assembly of HS2’s second 1,600-tonne tunnel boring machine (TBM)
  • The machine will start digging the second bore of the 3.5-mile Bromford Tunnel into Birmingham next spring
  • Joins existing TBM “Mary Ann” already 500m deep into first bore excavation
  • The majority of new TBM was reused from “Dorothy” after completing the previous HS2 tunnel
  • The 90-person crew will operate TBM boring 24/7 to hit 16 monthly timelines per bore
  • 41k concrete segments to line the completed tunnel, precision fabrication for safety
  • HS2 at peak construction with nearly 10k workers rapidly advancing infrastructure
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