Starting today and operating 24 hours a day, it will take around three years for the tunnel boring machine (TBM), called Florence, to dig the 10-mile long tunnel under the Chiltern hills.
At 170 metres in length, the 2,000 tonne TBM is also the largest ever used on a UK rail project. As is traditional, all TBMs are given female names, and Florence is named after Florence Nightingale – a name suggested by local children due to her residence at nearby Claydon House in Bucks.
A second machine ‘Cecilia’ will launch next month to excavate the second tunnel at the South Portal site. The delay between launching TBMs is usual as it creates a gap between the machines underground to minimise ground disturbance as they chew through the soil.
Designed specifically for the mix of chalk and flints under the Chilterns, the two identical TBMs will dig separate tunnels for north and southbound trains.
Each machine operates as a self-contained underground factory – digging the tunnel, lining it with concrete wall segments and grouting them into place at a speed of around 15 meters a day. Each tunnel will require 56,000 fibre-reinforced tunnel segments – which will all be made at the large building site just inside the M25 motorway.
A crew of 17 people will operate each TBM, supported by over 100 people on the surface, managing the logistics and maintaining the progress of the tunnelling operation.
Chalk excavated from the tunnels will be used for landscaping at the south portal site once construction is complete, creating chalk grassland habitats across 127 hectares of the southern Chiltern hills.
In total 64 miles of tunnels will be dug for the first phase of the HS2 railway between London and the West Midlands.
When it opens, the main aim of HS2 is to remove intercity trains from the existing railway so that much more capacity can be released for more regional and commuter trains between towns.
