HS2’s Florence and Cecilia TBMs reach Little Missenden

HS2 announced on Tuesday, August 8, that Florence and Cecilia, the two 2,000-ton tunnel boring machines (TBMs) had reached the Little Missenden ventilation shaft.

This event marks a significant milestone for the 16-kilometer (10 mile) long tunnels running under the Chilterns, as the Little Missenden shaft is the fourth out of five ventilation and emergency access shafts that exist along the route. It is also worth noting that this shaft is located at a length of about 75% of the Chiltern twin tunnel’s total one.

Florence and Cecilia were first launched approximately two years ago, in the summer of 2021, near the M25 in Buckinghamshire.

Both of the TBMs have a diameter of 10.26 meters and a length of 170 meters, while they are operating as self-contained underground factories. More specifically, they are lining 56,000 concrete segments, which will form the tunnel rings, while grouting them in place and digging forward.

The two TBMs have so far excavated about 2 million cubic meters of flint and chalk.

Finally, all five shafts have been excavated, while it has been known that a machinery headhouse will be constructed over the Little Missenden one, which will resemble local farm buildings.