The 125m-long TBM Elizabeth, named after the 19th century philanthropist Elizabeth Cadbury, was launched near the Warwickshire village of Water Orton in March 2024. It finished its journey at Washwood Heath.
Balfour Beatty Vinci (BBV) used two TBMs to dig the 5.6km-long Bromford tunnel that will carry high-speed trains under the M6 and eastern outskirts of the city. TBM Mary Ann broke through in May this year.
Together, Elizabeth and Mary Ann excavated more than 1.8 million tonnes of material and installed 5,804 concrete ring segments for the twin, eastbound and westbound tunnels. The spoil – made up of various grades of Mercia Mudstone – is being used to landscape the railway on the approaches to the city.
Yesterday’s breakthrough means excavation is now complete for the 45km of deep-bore tunnel between Old Oak Common in west London and the railway’s terminus at Birmingham Curzon Street. Construction teams are now mainly focused on internal walkways, ventilation shafts and cross passages.
Although the tunnel milestone is a significant achievement for the teams in Birmingham, other parts of the railway’s civil engineering are further behind.
HS2 Ltd chief executive Mark Wild is leading a comprehensive reset of the programme to deliver the railway in the most efficient way possible and for the lowest reasonable cost.
HS2 Ltd construction delivery director Alan Morris said he was “immensely proud of the men and women who have worked round the clock to bring our TBMs and their crews home safely”.
Eight TBMs have been used on the project so far, excavating 9.4 million tonnes of material. The 16.1km Chiltern Tunnel is the longest on the route, while the Northolt tunnels run for 13.5km from West Ruislip to Old Oak Common in west London. There is a short 1.6km twin-bore tunnel beneath Long Itchington Wood in Warwickshire.
Two more TBMs are expected to launch next year to begin digging the tunnels from Old Oak Common to HS2’s London Euston destination.
A short section of mined tunnel is also being dug between the Victoria Road Crossover Box and Old Oak Common.
Alongside these deep tunnels, HS2 is also delivering around 8km of shallow cut-and-cover tunnels in rural areas such as Burton Green in Warwickshire, Chipping Warden in West Northamptonshire and Wendover in Buckinghamshire.
During their 18-month mission, the team building the Bromford tunnel worked at depths of up to 40m. They navigated the two TBMs under the M6 motorway, key National Grid infrastructure and the River Tame – which they crossed four times, with an overburden as low as 5m.
TBM Elizabeth will now be removed from the tunnel to allow work to progress on the concrete finishing works, base slabs, and emergency and maintenance walkways.
Balfour Beatty Vinci tunnelling director Jules Arlaud said everyone connected with the project felt a sense of achievement and pride and the breakthrough followed years of planning and preparation.
“This has allowed us to guide Elizabeth safely and successfully underneath complex ground conditions and critical live infrastructure. A breakthrough is always a unique moment, and it marks the culmination of exceptional engineering, dedication, and collaboration,” he said.
As well as being the arrival point for the two Bromford tunnel TBMs, Washwood Heath will also become the nerve centre for HS2’s operations. HS2’s Depot and Network Integrated Control Centre will be built next to the tunnel portal. Here trains will be serviced and stored, and the real-time operation of the railway will be controlled.
Washwood Heath is one of three key HS2 sites in the West Midlands, alongside the two new stations that will be built in Birmingham and Solihull.
