Cecelia is set to complete its journey in the coming weeks. Credit: HS2.

The UK’s High Speed 2 (HS2) railway project has achieved a milestone as its first tunnel boring machine (TBM) broke through the Chiltern Hills after nearly a three-year, 16km journey. 

The 32-mile tunnel for HS2, Great Britain’s new railway, will connect London Euston with Birmingham, reducing travel times. 

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The twin-bore Chiltern tunnel, stretching from the South Portal near the M25 motorway to South Heath in Buckinghamshire, is being constructed using two identical TBMs. 

The 2,000-tonne TBM named ‘Florence’, one of ten machines excavating the tunnel, initiated the excavation in May 2021 and has been integral in constructing the twin-bore Chiltern tunnel.  

The second TBM, ‘Cecilia’, is anticipated to complete its journey in the forthcoming weeks.  

These parallel tunnels will facilitate north and southbound trains, enhancing the capacity of the existing West Coast Main Line. 

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Designed to navigate the Chiltern geology, each TBM operates as an underground factory, simultaneously excavating the tunnel and installing 56,000 precast concrete segments.  

Align project director Daniel Altier said: “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.”

Each TBM requires a crew of 17 supported by more than 100 surface personnel ensuring the smooth continuation of the tunnelling operation. 

The latest development comes after Buckinghamshire Council approved the construction of HS2’s advanced maintenance hub in Calvert, Buckinghamshire, earlier this week.