HS2 has announced that Florence and Cecilia – the two giant tunnelling machines digging HS2's longest tunnels - have passed Amersham.

The enormous 2,000 tonne machines have spent almost two years excavating the twin tunnels between the M25 and South Heath in Buckinghamshire that 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 the Buckinghamshire town. A 'headhouse' will be built on top of the shaft to house safety equipment, with a flint-faced boundary wall and a pre-patinated zinc roof to help match the natural tones of the surrounding landscape.

Once complete, trains will pass through the tunnel at speeds of up to 320km/h, providing zero carbon journeys between London, Birmingham and the north while freeing up capacity on the existing rail network.