HS2’s first two Tunnel Boring Machines (TBMs) have arrived in the UK ahead of starting tunneling work next to the M25 early next year. They were built in Germany by Herrenknecht and were shipped in parts to the UK. The last shipment has now arrived and work can start reassembling the giant kit machine so that it can start tunnelling next year.
The two 170m-long TBMs – the largest ever used on a UK rail project – will be used to dig the 10-mile-long tunnels that will head out of North-West London and underneath the Chilterns. The 10-mile-long ‘twin bore’ Chiltern tunnel will be the longest on the project and will take around three years to dig. The two identical TBMs, named as is the convention, after females, will dig separate tunnels for north and southbound trains, with Florence set to launch first and Cecilia to follow a few weeks behind.
TBMs are always designed specifically to each task to take in account local soil conditions, and in this case, they will need to tunnel through ground mainly made from a mix of chalk and flints under the Chilterns. The TBMs will convert the spoil into a slurry which will be pumped back to the south portal site where it will be treated before being used for landscaping on-site.
Each machine operates as a self-contained underground factory, which as well as digging the tunnel, will also line it with concrete wall segments and grout them into place as it moves forward at a speed of 15 metres a day. Each tunnel will require 56,000 segments – which will all be made on site. A crew of 17 people will operate each TBM, working in shifts to keep the machines running 24/7. They will be supported by over 100 people on the surface.
The names of the two TBMs were suggested by students at Meadow High School in Hillingdon and The Chalfonts Community College, Buckinghamshire, which are close to the tunnel launch site. They were inspired by Florence Nightingale, the founder of modern medicine, and pioneering astronomer and astrophysicist, Cecilia Payne-Gaposchkin.