Tunnelling passes 75% mark on HS2’s longest tunnels

The 2,000 tonne Herrenknecht machines, Florence and Cecilia, have spent two years excavating the twin tunnels between the M25 and South Heath in Buckinghamshire for the high-speed railway.

As well as digging and lining the tunnels, which are 90m below ground at the deepest point, engineers have also completed the excavation of five shafts that will provide ventilation and emergency access near Chalfont St Peter, Chalfont St Giles, Amersham and the 35m-deep Little Missenden with an intervention shaft at Chesham Road.

The news comes just weeks after Buckinghamshire Council granted planning consent for the North Portal, meaning all major design elements now have consent.

“The huge progress that Florence and Cecilia have made would not have been possible without a huge team in support – manufacturing the tunnel segments, excavating the vent shafts and I’d like to thank everyone involved,” said HS2 Ltd’s project client, David Emms.

The two TBMs are operated by Align – a joint venture of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.

“Both TBMs reaching our fourth shaft at Little Missenden is a great achievement for not only the tunnelling team and the team involved in excavating and preparing the shaft, but also the supporting teams on the surface at the South Portal, manufacturing the concrete segments required to line the tunnel and processing the spoil from the tunnels,” said Align project director Daniel Altier.

“In particular I would like to pay credit to Align Shafts team, working with our supply chain partners and Keltbray, who have been working over the last few months to ensure the shaft is ready for the arrival of Florence and Cecilia.”   

Approximately 2.7 million m3 of material – mostly chalk and flint - will be excavated during the construction of the tunnels and used for landscaping. More than 2 million m3 have been excavated since the TBMs were launched in summer 2021.

HS2 currently has five TBMs in the ground, with a further five due to be launched over the coming years. Together they will create 103km of tunnel between London and the West Midlands, including major tunnels on the approach to London and Birmingham.