The first two tunnel boring machines (TBMs) that will excavate the twin-bore Chiltern tunnel for HS2 are almost complete at the factory in Germany, .
They will be operated by HS2’s main works contractor, Align JV – a joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
The huge 2,000 tonne machines – which have been built by world-leading German tunnelling specialists Herrenknecht – will be disassembled for shipping and will arrive at Align’s main site at Chalfont Lane, just inside the M25 to the west of London, later this year.
In line with tradition, the TBMs have been named. Florence and Cecilia were the names chosen by public vote, with Florence (after nursing pioneer Florence Nightingale) taking 40 per cent of the vote and Cecilia (astronomer and astrophysicist Cecilia Payne-Gaposchkin) 32 per cent. The names were suggested by students at Meadow High School in Hillingdon and the Chalfonts Community College, Buckinghamshire.
Daniel Altier, Align project director, said: “Florence and Cecilia incorporate the latest technology, which will be essential to ensure an efficient and safe excavation of the twin-bore tunnel. This will be the first time that some of the innovations we are introducing will have been used on any TBM worldwide.
“With STEM subjects a top priority in many schools, we are delighted that local schools have had the opportunity to get involved by selecting the names and we hope schoolchildren across the UK will be keen to monitor the progress of our TBMs over the next three years.”
‘Florence’ is set to be launched early next year to begin digging the 10-mile-long Chiltern tunnel. ‘Cecilia’ will launch around a month later and will dig the other bore of the twin-bore tunnel.
Both 170-metre-long machines are specifically designed for the mix of chalk and flint they will encounter under the Chilterns. Operating a ‘continuous boring’ technique, they are expected to take around three years to excavate the tunnels, which will be lined with concrete as they go.
The actual size of the TBM cutterhead, which will bore the tunnels is 10.26 metres. Once lined with a ring of concrete segments, each measuring two metres by four metres and weighing 8.5 tonnes, the bore is reduced to the finished diameter of 9.1 metres.
A total of 112,000 concrete segments will be used, installed by the TBM as part of the tunnelling process. They will be manufactured in a special plant adjacent to the site.
The TBMs will mix the tunnelling spoil with water to form a slurry, which will be pumped back to the main site where it will be treated before being used for landscaping on-site, removing the need for additional HGV movements to remove it.