Two 170m HS2 tunnel boring machines have created another underground section of the high speed line in the Chilterns, by reaching the ventilation shaft at Great Missenden.

‘Florence’ and ‘Cecilia’ are now three quarters of the way through their 16km drive under the Chilterns, having spent the last two years excavating the two bores between the M25 and South Heath, which is roughly 2km east of Great Missenden.

Designed for the geology of the Chilterns, the first TBMs were launched in the summer of 2021 from a site near the M25 and have already excavated 2 million cubic metres of chalk and flint.

Engineers have also completed 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.

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 landmark 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.

The tunnel will form part of Phase 1 between London and Birmingham, which has been given a ‘red’ rating by the Infrastructure Projects Authority, meaning that the London to Birmingham and Birmingham to Crewe sections are considered to be ‘unachievable’.

Even so, HS2 Ltd pointed out that ‘construction was now hitting a peak, with “work intensifying and huge civil engineering structures taking shape”’.

HS2 Ltd’s project client David Emms said: ‘HS2 will transform rail journeys between London the midlands and the north, and free up space on the existing network for more freight and local services. We’re seeing great progress on the tunnel, which will take our trains deep under the Chiltern hills, safeguard the woodlands and wildlife habits above and significantly reducing disruption to communities.

‘The huge progress that Florence and Cecilia have made would not have possible without a huge team in support - manufacturing the tunnel segments, excavating the vent shafts and I’d like to thank everyone involved.’

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