HS2 has announced that the two giant tunnelling machines excavating the high speed rail project's longest tunnels, have passed the halfway point on their 10 mile journey under the Chilterns.

'Florence' and 'Cecilia', the enormous 2,000 tonne machines, have spent the last 18 months excavating the twin tunnels between the M25 and South Heath in Buckinghamshire that will help protect the environment while improving connections between London, Birmingham and the North.

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 Chesham Road. They also recently completed the first breakthrough from a cross passageway to the shaft at Chalfont St Peter.

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More than 1.3 million cubic metres of chalk and flint – enough to fill more than 500 Olympic swimming pools - has been excavated and will be used as part of an ambitious chalk grassland restoration project at the south portal of the tunnel. This will see the creation of 127 hectares of new landscaping, wildlife habitat and biodiverse chalk grassland.

Once complete, the Chiltern tunnels will carry high speed trains between London and the North at speeds of up to 200mph (320km/h), helping to improve connections, free up space for more freight and local trains on the existing railway and provide zero carbon journeys for people across the UK.