The two 2,000-tonne tunnel boring machines (TBMs) have spent the last 18 months excavating twin tunnels between the M25 and South Heath in Buckinghamshire for the new London-Birmingham high-speed rail line.

As well as digging and lining the tunnels, lead contractor on this section, Align, has also completed the excavation of five shafts that will provide ventilation and emergency access near Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden and Chesham Road. Align also recently completed the first breakthrough from a cross passageway to the shaft at Chalfont St Peter.

More than 1.3 million cubic metres of chalk and flint has been excavated on this section so far and will be used as part of a chalk grassland restoration project at the south portal of the tunnel.

Martyn Noak, head of tunnel engineering for client organisation HS2 Ltd, said: “The whole team has put in a fantastic effort over the last year-and-a-half and I’d like to congratulate the crews of both Florence and Cecilia for passing this important tunnelling milestone and thank them for all their hard work.”

Align, a joint venture of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick, is responsible for the Chiltern tunnel and nearby Colne Valley Viaduct. A crew of 17 people from subcontractor TG Tunnelling operates each TBM, working in shifts to keep the machines running 24/7. They are supported by more than 100 people on the surface, managing the logistics.

More than 56,000 fibre-reinforced tunnel lining segments have been installed so far, with each one made on site in a dedicated temporary pre-cast factory.

Didier Jacques, Align’s underground construction director, described it as “a great team effort”.

As well as the Chiltern tunnels, HS2 also recently launched two TBMs to begin the project’s London tunnels and celebrated the first breakthrough with the completion of the first of two tunnels under Long Itchington Wood in Warwickshire.

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