A giant tunnelling machine digging HS2’s approach into Birmingham has broken through at Washwood Heath, marking the completion of all deep tunnel excavation between London and the West Midlands.

The 125-metre-long machine, named Elizabeth after local philanthropist Elizabeth Cadbury, began its journey near Water Orton in March 2024. It is one of two identical tunnel boring machines (TBMs) used to carve the 3.5-mile Bromford Tunnel under the M6 and the city’s eastern outskirts. The first, Mary Ann, completed her drive earlier this year.

Together, the two TBMs have excavated more than 1.8 million tonnes of Mercia Mudstone and installed nearly 6,000 concrete ring segments to form the twin tunnels. The spoil is being reused to shape the landscape on the railway’s approach to the city.

The breakthrough means that all 23 miles of deep-bore tunnelling between Old Oak Common in west London and Birmingham Curzon Street are now complete. Work will now focus on fitting internal walkways, ventilation shafts and cross passages.

Once operational, HS2 is expected to cut journey times between London and Birmingham and free up capacity on the existing West Coast Main Line for additional local and freight services.

Mark Wild, HS2 Ltd’s chief executive, said a programme reset is underway to ensure the railway is delivered efficiently and cost-effectively.

Alan Morris, HS2 Ltd’s construction delivery director, described the breakthrough as “a major milestone”, praising the engineers and crews who have worked around the clock.

“All eight of the TBMs digging our tunnels between Old Oak Common and Curzon Street have now broken through,” he said. “The focus now turns to internal concrete work, ventilation shafts and cross passages.”

Eight TBMs have been used on HS2 so far, excavating a combined 9.4 million tonnes of material. The longest tunnel, beneath the Chiltern Hills, stretches 10 miles, while the Northolt tunnels run 8.4 miles in west London. Two further TBMs are due to launch next year to begin tunnelling towards Euston.

The Bromford Tunnel has been delivered by HS2’s main works contractor, Balfour Beatty VINCI (BBV). Around 450 people have been involved in the complex year-and-a-half operation, which saw the 1,600-tonne TBMs navigate beneath the M6, National Grid infrastructure and the River Tame – crossed four times with as little as five metres of clearance.

Jules Arlaud, BBV’s tunnelling director, said the breakthrough marked “the culmination of exceptional engineering, dedication and collaboration”.

“Our expert team has worked tirelessly for 19 months to guide Elizabeth safely through challenging ground and critical infrastructure,” he said.

Washwood Heath, now the arrival point for both TBMs, will also host HS2’s main depot and Network Integrated Control Centre, overseeing train servicing and operations. Alongside Curzon Street and Interchange Station in Solihull, the site forms one of three major HS2 hubs in the region, which are already attracting investment expected to add around £10 billion to the West Midlands economy over the next decade.