Tunnel progress as HS2’s ‘Florence’ and ‘Cecilia’ reach Little Missenden

Thursday, 17 August 2023 13:03

‘Florence’ and ‘Cecilia’ – the two giant tunnelling machines digging HS2’s longest tunnels - have reached the Little Missenden ventilation shaft, more than three quarters of the way through their 10 mile drive under the Chilterns.

The enormous 2,000 tonne machines have spent two years excavating the twin tunnels between the M25 and South Heath in Buckinghamshire that will help improve 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.

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 and Little Missenden with an intervention shaft at Chesham Road.

The 35m deep shaft near Little Missenden – which the TBMs have now reached – is next to the A413 about half a mile from the Buckinghamshire village.

A ‘headhouse’ will be built on top of the shaft to house ventilation and safety equipment, designed to resemble local farm buildings with new planting to help blend it into the surrounding landscape.

The news comes just weeks after planning consent was granted by Buckinghamshire Council for the North Portal of the tunnel under Schedule 17 of the HS2 Act, meaning that all major design elements now have consent.