The second of two tunnel boring machines has been launched from just inside the M25 to dig tunnels for HS2 under the Chilterns.

The second tunnel boring machine (TBM), called Cecilia after Cecilia Payne-Gaposchkin, an astronomer, started a month after the first, called Florence, named after Florence Nightingale. Despite starting second, Cecila will run slightly faster, aided by geological data fed back from Florence, meaning that both machines are due to breakthrough at the end of the tunnels at around the same time.

Designed specifically for the mix of chalk and flints under the Chilterns, the two TBMs move at a speed of up to 15 metres a day. Each machine operates as a self-contained underground factory – digging the tunnel, lining it with concrete wall segments and grouting them into place. Each tunnel will require 56,000 fibre-reinforced 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, 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 wildlife-rich chalk grassland habitats across 127 hectares of the southern Chiltern hills.

In total there will be ten tunnel boring machines (TBMs) working to create 64 miles of tunnel between London and the West Midlands.