Just days before Christmas,
HS2 Ltd confirmed that ‘Florence’ and ‘Cecilia’ — the two giant 2,000-tonne tunnelling machines digging the project’s longest tunnels — had reached the Chesham Road intervention shaft and were on track to complete their 10-mile journey under the Chilterns early this year, being 90% of the way through their 2.5-year drive between the M25 and South Heath in Buckinghamshire.
In total, HS2 will require 64 miles of tunnelling, with five tunnel-boring machines (TBMs) already in the ground, three more ready to go, and another two due to be delivered next year. Each Chiltern TBM is a 170m-long self-contained underground factory, digging the tunnel, lining it with concrete segments to form rings and grouting them into place as it moves forward. These TBMs, which were designed specifically for the geology of the Chilterns and launched in Summer 2021 from a site near the M25, have already excavated about 2.8 million cubic metres of chalk and flint.
The 42m-deep shaft near Great Missenden, which the TBM has now reached – is largely hidden behind a hedge and line of mature oak trees next to the B485. A ‘headhouse’ to be built on top of the shaft will be designed to resemble local farm buildings, along with new plantings to help blend it into the surrounding landscape. The Chesham Road shaft (there are four other four shafts on-route for both access and ventilation) will only be used for emergency access.
The two TBMs are operated by Align (a joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick); each machine has a crew of around 15 people working in shifts, and is supported by over 100 people on the surface, managing the logistics and maintaining the smooth progress of the tunnelling operation.
Didier Jacques, Align’s underground construction director, said: “With our first TBM — Florence — having reached our fifth shaft at Chesham Road and our second TBM — Cecilia — due to reach the shaft shortly, this a great achievement for not only the tunnelling team but also the supporting teams on the surface at the South Portal, where they are manufacturing the concrete segments required to line the tunnels and processing the spoil from the tunnels. We are looking forward to continuing the good progress with the TBMs, which are due to complete their drives early this year.”