The two giant tunnelling machines 'Florence' and 'Cecilia' digging the longest tunnels of the High Speed Rail project have passed the halfway point of their 10-mile journey under the Chilterns. The huge 2,000-tonne machines have been digging a pair of tunnels between the M25 and South Heath in Buckinghamshire for the past 18 months. As well as digging and lining the tunnels, engineers have also completed the excavation of five shafts to provide ventilation and emergency access.
The first five miles have produced 1.3 million cubic meters of chalk and flint, enough to fill more than 500 Olympic swimming pools. The material will be used as part of an ambitious chalk grassland restoration project at the south portal of the tunnel. When complete, the Chiltern tunnels will carry high-speed trains between London and the North at speeds of up to 320km/h, helping to improve connectivity, freeing up space on the existing railway for more freight and local trains, and providing emission-free travel for people across the UK.
“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. Once complete, HS2 will offer low carbon journey options linking London with the major cities of the north and releasing capacity for more freight and local trains on our existing mainlines,” said Martyn Noak, HS2 Ltd's Head of Tunnel Engineering.
Two identical TBMs, specially designed for the chalk and flint mix under the Chilterns, are excavating separate tunnels for the northbound and southbound trains. Each machine works as a self-contained unit - excavating a tunnel, lining it with concrete wall segments, and grouting them into place at a rate of around 15 meters per day. More than 56,000 precision-engineered, fiber-reinforced segments have been installed to create the tunnel walls - each manufactured on-site in a dedicated temporary precast factory. The machines are working continuously - each TBM is manned by a crew of 17 working in shifts. They are supported on the surface by more than 100 people who manage the logistics and keep the tunnelling running smoothly.
