Second Chilterns TBM breaks through

Cecilia arrives!

Having set off from near Maple Cross in June 2021, TBM Cecilia has now completed her 10-mile drive and reunited with her twin sister machine, Florence, who reached the site near Wendover on 27th February after completing her adjacent tunnel drive.

Between them, the two 2,000-tonne machines have built the twin bore tunnel at depths of up to 80 metres and excavated three million cubic metres of chalk. They have each installed 56,000 pre-cast concrete tunnel segments, grouting them into place and moving forward at an average speed of 16 metres per day.

HS2 Ltd’s head of civil works for this section of the route, Mark Clapp, said: “Cecilia’s arrival completes excavation of HS2’s 10-mile twin-bore tunnel, but it’s only the end of the first chapter in the story of building Britain’s high-speed railway under the Chiltern Hills. Several years of intensive, world class engineering lie ahead of us to complete the tunnels’ four ventilation shafts plus headhouses; install the mechanical and electrical plant and machinery, slab track and overhead electrical wires before trains begin passing through at 200mph.”

The Herrenknecht TBMs were operated by HS2’s main works contractor, Align – a joint venture of Bouygues, Sir Robert McAlpine, and VolkerFitzpatrick.

Align’s underground construction director, Didier Jacques, said: “Ten miles is a long drive for a TBM, with a typical average being around three miles. The complexity and technically challenges of completing such a long drive for both our TBMs has been significant. However, I am delighted that as a team, we have risen to the challenge.

“Both TBMs were designed in partnership with Herrenknecht and incorporate 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.”

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