It comes after HS2’s first giant tunnelling machines arrived in the UK in December last year. To create the Chiltern tunnels – the longest on HS2 – the tunnel boring machines (TBMs), named Florence and Cecilia, will work non-stop for about three and a half years when they launch in early summer. The two tunnels will go as deep as 80 metres below the ground to reduce the impact of the high-speed trains on communities and countryside on the route and their internal diameter will be 9.1 metres, providing enough space for emergency walkways on both sides of the track. Made of high-performance fibre-reinforced concrete, the segments are being produced at what will be the south portal of the tunnels to avoid putting extra HGVs on local roads and to ensure a steady supply of segments for the TBMs.
Some of the wall sections being produced at the factory (David Hares)
A worker at the temporary factory. (David Hares)
Once construction is complete, the pre-cast factory and the rest of the south portal site will be cleared, with the chalk excavated from the tunnels used to landscape the site and create chalk grassland and other wildlife habitats. HS2 Ltd’s C1 project director, Rohan Perin said: “The start of production at the tunnel wall precast plant is a major milestone as we countdown to the launch of our first TBMs later this year. By casting all 112,000 segments on site we can significantly reduce the number of HGVs on local roads and reduce the amount of disruption for local residents. Once complete, the 10-mile-long tunnels under the Chilterns will also significantly reduce the impact of the project on the local environment, with material from tunnels used to create new species rich chalk grassland.” Construction of the Chiltern tunnel, and nearby Colne Valley Viaduct, is being led by HS2’s main works contractor, Align JV – a joint venture made up of three companies, Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick. Didier Jacques, Align’s Underground Construction Director added: “We are using Steel Fibre Reinforced Concrete (SFRC) in the segments due to the improved ductility and durability it offers. The SFRC segments are also easier to fabricate. Once in the moulds we are using robots to polish the concrete, a task that was previously manual, to improve the quality and consistency of the final product. With seven segments in each ring, we will be producing a total of 160 rings ahead of launch of the first TBM later this year.”