An enormous machine being used to dig HS2’s Birmingham approach tunnels has broken through, marking the completion of major tunnel excavation between London’s Old Oak Common and the West Midlands.

The 125-metre-long tunnel boring machine - named Elizabeth after the 19th century philanthropist Elizabeth Cadbury - was launched near the Warwickshire village of Water Orton in March 2024. It arrived at Washwood Heath this morning (13 October).

Two identical machines were used to dig the 3.5-mile long Bromford tunnel that will carry high speed trains under the M6 and eastern outskirts of the city, with the first one – Mary Ann – breaking through earlier this year.

Together, Elizabeth and Mary Ann have 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.

The milestone means all the excavation is now complete for the 28 miles 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.

Mark Wild, HS2 chief executive, is now leading a comprehensive reset of the programme to deliver the railway in the most efficient way possible and for the lowest reasonable cost.

Alan Morris, HS2 construction delivery director, said: “Today’s breakthrough is a major milestone for the tunnelling team here in Birmingham and for the HS2 project. All eight of the TBMs digging our tunnels between Old Oak Common and Curzon Street have now broken through, which means that the focus is now on the internal concrete work, ventilation shafts and cross passages.

“I’m immensely proud of the men and women who have worked round the clock to bring our TBMs and their crews home safely, and I look forward to seeing more progress inside the tunnels in the years ahead.”

Each TBM is an underground factory – working 24/7 to excavate, install the concrete ring segments that form the walls and grout them into place as it moves forward at an average speed of around 10 metres per day.

Two more TBMs are expected to launch next year to begin digging the tunnels from Old Oak Common to HS2’s final destination, London Euston.

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 five miles of shallow ‘cut-and-cover’ tunnels in rural areas such as Burton Green in Warwickshire, Chipping Warden in West Northamptonshire and Wendover in Buckinghamshire.

The Bromford tunnel is being delivered by HS2’s main works contractor Balfour Beatty VINCI (BBV) with a team of more than 450 people involved in the complex logistical operation required to keep the TBMs moving around the clock.

During their year-and-a-half-long mission, the team on board the 1,600-tonne machines worked at depths of up to 40 metres. They skilfully navigated Elizabeth and Mary-Ann under the M6 motorway, key National Grid infrastructure and the meandering River Tame – which they crossed four times, with a headspace as low as five metres.