Historic breakthrough for HS2’s longest tunnel

27th February 2024
Paige West

Today marks a significant achievement for the HS2 project as the first colossal tunnelling machine, launched nearly three years ago, completed its 10-mile journey beneath the Chilterns, carving out the project's lengthiest tunnel.

This 2,000-tonne Tunnel Boring Machine (TBM), named ‘Florence’, leads the fleet of 10 TBMs tasked with excavating the 32 miles of tunnels for the new railway that will connect London Euston with Birmingham, having initiated its operation in May 2021.

Rail Minister Huw Merriman said: “This ground-breaking moment for HS2 demonstrates significant progress on the country’s largest infrastructure project, with ‘Florence’ paving the way for faster, greener journeys between London and Birmingham while supporting hundreds of jobs and apprenticeships along the way.

“Today’s breakthrough of HS2’s longest tunnel highlights the momentum behind the project and the achievement is testament to the hard work and dedication of the 450-strong team helping deliver the line that will transform rail travel for generations to come.”

This breakthrough signifies a pivotal moment for HS2, set to significantly reduce travel times between the UK's two largest cities and alleviate congestion on the West Coast Main Line by providing additional capacity for local services.

The Chiltern tunnel, constructed using two identical TBMs, including ‘Florence’ and its counterpart ‘Cecilia’ (expected to complete its journey shortly), runs from the South Portal near the M25 to South Heath in Buckinghamshire. These parallel tunnels will facilitate north and southbound train traffic.

Custom-designed for the Chilterns' geological conditions, each TBM operates like an underground factory, simultaneously excavating the tunnel, lining it with pre-cast concrete segments, and securing them in place, advancing at an average rate of 16m per day.

The construction also involves four TBMs for the London approach tunnels and two for Birmingham’s Bromford tunnel, with preparations for launching two additional machines for the Euston tunnels already in progress.

This event follows HS2's announcement of new research predicting a £10 billion economic uplift for the West Midlands over the next decade, spurred by the high-speed rail's introduction and the development it will bring to the surrounding areas of the two station sites.

The TBMs, constructed by Herrenknecht in Germany, were launched by HS2’s main works contractor, Align—a collaboration of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick. Operating these machines is a team of approximately 17 per shift, supported by over 100 surface personnel, ensuring 24/7 operation and seamless progress.

Over the last three years, more than 450 individuals have contributed to the tunnel construction and support operations. This includes a dedicated team that produced over 112,000 concrete tunnel wall segments and a team responsible for processing the excavated material.

The three million cubic metres of chalk and other materials extracted are being repurposed for a large-scale grassland restoration project at the south portal, creating new wildlife habitats and chalk grassland across 127 hectares.

The tunnel's construction, reaching depths of up to 80m and passing beneath significant infrastructures without adversely affecting water quality, showcases the project's commitment to environmental conservation and engineering excellence.

Furthermore, Align is progressing on the UK's longest railway bridge, the Colne Valley Viaduct, with more than two-thirds of the deck construction completed, underscoring the scale and ambition of the HS2 project.

HS2 Ltd Executive Chairman, Sir Jon Thompson, said: “Today is an incredible day of HS2 and I’d like to thank the hundreds of people who’ve worked so hard over many years to make it happen. Once complete, HS2 will dramatically improve journeys between our two largest cities and also free up space on the existing mainline for more local trains.

“We’ve still got a lot of work to do, but historic moments like today really underline the huge amount of progress that’s been made and the fantastic engineering skills we have on the project.”

Align’s Project Director, Daniel Altier said: “The typical drive for a TBM is 5-6km and therefore the challenges in completing at 16km drive should not be underestimated.

“Florence and her sister TBM Cecilia were designed in partnership with Herrenknecht. They incorporate a number of innovations and technologies that have been introduced on TBMs in the UK for the first time, to enhance performance and safety. This includes ‘semi-continuous boring’, allowing our TBMs to build the rings that line the tunnels without pausing.

“The mining of the tunnel is a fantastic achievement for not only the Align tunnelling team but also the earthworks team who have managed chalk excavated from the tunnels and placed on site, along with many other supporting functions. I would also like to acknowledge our supply chain partners, including TGT that provided the teams to operate the TBMs and MS with whom we designed and operated the slurry treatment plant, with 24 filter presses it is the largest in the world.’”

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