TWO GIANT tunnelling machines digging HS2's longest tunnels have passed Amersham, five-and-a-half miles into their 10-mile drive under the Chilterns.

The machines dubbed ‘Florence’ and ‘Cecilia’ are enormous 2,000 tonne machines that have spent almost two years excavating the twin tunnels between the M25 and South Heath in Buckinghamshire.

HS2 said it will help the high speed rail project protect the environment while improving connections between London, Birmingham and the North.

Each machine is a 170m long self-contained underground factory, digging the tunnel, lining it with 56,000 concrete segments to form rings and grouting them into place as it moves forward.

Designed specifically for the geology of the Chilterns, the first TBMs were launched in Summer 2021 from a site near the M25 and have excavated more than 1.8 million cubic metres of chalk and flint.

As well as digging and lining the tunnels, engineers have 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 an intervention shaft at Chesham Road.

The 44m deep shaft at Amersham – which the TBMs have now passed - will be in the middle of a road junction just outside a Buckinghamshire town. 

Martyn Noak, HS2 Ltd’s Head of Tunnel Engineering, said: “The Chiltern tunnel will take HS2 underground and safeguard the woodlands and wildlife habits above the tunnel as well as significantly reducing disruption to communities during construction and operation of the new railway.

“I’ve been very impressed with the progress made by Florence and Cecilia as they make their way unseen beneath the Chiltern Hills.  It’s great to see how much progress they and the teams excavating the five shafts have made and I’d like to thank everyone involved in getting us this far.”

Each machine has a crew of 17 people, working in shifts and supported by over 100 people on the surface, managing the logistics and maintaining the smooth progress of the tunnelling operation.

Coralie Peroux, Tunnel Manager, Align said: "‘Florence and Cecilia reaching our third shaft at Amersham 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.

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