GIANT HS2 tunnelling machines reached a milestone under the Chiltern Hills.

The 2,000 tonne tunnelling machines Florence and Cecilia have now passed halfway through the 10-mile-long Chiltern twin tunnel through Buckinghamshire countryside. 

The machines’ journey to connect the M25 and South Heath has taken 18 months, and excavated enough chalk and flint to fill more than 500 Olympic swimming pools – equal to 1.3 million cubic metres.

HS2’s head of tunnel engineering Martyn Noak said: “This tunnel will take HS2 underneath the Chiltern hills, safeguarding the woodlands and wildlife habits above ground as well as significantly reducing disruption to communities during construction and operation.”

Bucks Free Press: Tunnellers celebrate first access from a vent shaft to the tunnelTunnellers celebrate first access from a vent shaft to the tunnel (Image: HS2 Ltd)

Engineers for the high speed railway have also completed excavation of five shafts providing ventilation and emergency access near Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden and Chesham Road.

The excavated materials will be used to create 127 hectares of new landscaping, wildlife habitat and biodiverse chalk grassland as part of grassland restoration project at the south portal of the tunnel. 

Bucks Free Press: Chiltern tunnel with its crosspassageway on the rightChiltern tunnel with its crosspassageway on the right (Image: HS2 Ltd)

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Both tunnelling machines need a crew of 17 people to operate them in shifts 24 hours a day. 

Mr Noak said: "It’s great to be able to celebrate the half-way point of this 10-mile long tunnel. The whole team has put in a fantastic effort over the last year-and-a-half and I’d like to congratulate the crews of both Florence and Cecilia for passing this important tunnelling milestone and thank them for all their hard work.”