Giant tunnel boring machines, affectionately named 'Florence' and 'Cecilia', have reached a milestone in the HS2 high-speed rail project by reaching the Little Missenden ventilation shaft. This achievement means they are more than 75% of the way through their 10-mile journey beneath the Chiltern hills.
Each tunnel boring machine (TBM), spanning 170 meters in length, operates as a self-contained subterranean factory. As they advance, they excavate the tunnel, lining it with approximately 56,000 concrete segments to create rings and grouting them in place. Designed specifically for the geology of the Chilterns, these TBMs have already excavated around 2 million cubic metres of chalk and flint since their launch in the summer of 2021.
In addition to excavating and lining the tunnel, engineers have successfully completed the construction of five ventilation and emergency access shafts near key locations including Chalfont St Peter, Chalfont St Giles, Amersham and Little Missenden. The latter shaft, which the TBMs have now reached, is located close to the village of Little Missenden.
Approximately 2.7 million cubic meters of chalk and flint are being excavated during tunnel construction and reused for landscaping. With five TBMs already in operation and five more, due to start in the coming years, HS2 will create an extensive network of tunnels stretching 64 miles between London and the West Midlands.
“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,” said David Emms, HS2 Ltd’s Project Client.
