Machine digging HS2’s longest tunnel breaks through in Buckinghamshire

Workers at the Chiltern Tunnel breakthrough site ahead of digging machine Florence completing HS2’s longest tunnel. Credit: PA Wire/PA Images

The machine digging HS2’s longest tunnel has completed its 10-mile journey under the Chiltern Hills.

Florence, named after nurse Florence Nightingale, was greeted with fireworks and cheers from hundreds of HS2 workers who gathered to witness the moment near South Heath, Buckinghamshire, on Tuesday.

It was launched in May 2021 near Rickmansworth, Hertfordshire.

The machine dug one of a pair of tunnels with a depth of up to 80 metres that will be used for HS2 trains travelling between London and Birmingham.

A second identical machine will break through in the coming weeks.

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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.”

The move completes a 10-mile journey under the Chiltern Hills, in North Portal, near South Heath, Buckinghamshire Credit: Aaron Chown/PA

HS2 Ltd described Florence as an “underground factory” with a crew of around 17 people working in shifts to keep it running constantly.

It excavated the tunnel, lined it with 56,000 pre-cast concrete segments and grouted them into position, moving at an average speed of 16 metres per day.

Florence, which has a diameter of 10.25 metres, will be dismantled over the coming weeks.

Some large parts will be reused in other tunnel boring machines (TBMs) but many will be scrapped.

The three million cubic metres of chalk and other material removed during the tunnelling is being used for a grassland restoration project at the site where the machines were launched.

Preparations are also under way for the launch of two more machines to excavate tunnels between Old Oak Common and Euston in the capital.

Workers cheered the completion of the project Credit: Aaron Chown/PA

HS2 Ltd executive chairman Sir Jon Thompson said: “Today is an incredible day for 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.”

HS2 Ltd project client David Emms, who is responsible for the section of the route that includes the tunnel, paid tribute to the workers for their “immense feats of engineering”.

He said: “HS2 remains the biggest infrastructure project in the UK.

“From tunnels to train stations to structures and systems, the scale and ambition of what we are delivering is unmatched.

“What we are achieving today has helped to set new standards for the construction industry in the UK and around the world.

“Not only that, rail travel for the future is being set by us as well.”

Four similar TMBs are being used for tunnels on the approach to London, while another two will work on Birmingham’s Bromford tunnel.

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