The second tunnel boring machine (TBM) digging the future HS2 railway tunnels under the Chilterns has finished its job – meaning the two 10-mile tunnels have been completed and are now ready for fitting out.
Cecilia TBM breakbrough (c) HS2
Named Cecilia, the TBM has driven for 10 miles underground from just inside the M25 motorway to a site near the Buckinghamshire town of Wendover, and is the second TBM to complete the tunning work.
Between them, the two 2,000 tonne machines have built the twin bore tunnel at depths of up to 80 metres and excavated three million cubic metres of chalk. Each machine operates like an underground factory, able to excavate the tunnels and line them with 56,000 pre-cast concrete tunnel segments, grouting them into place and moving forward at an average speed of 16 metres per day.
When HS2 is operational trains will travel through the Chiltern tunnel – the line’s longest – at speeds of up to 200mph, helping to almost halve journey times between Britain’s two largest cities.
HS2’s head of civil works for this section of the route, Mark Clapp, said: “Today is a remarkable achievement for all concerned. Cecelia’s arrival completes excavation of HS2’s 10-mile twin-bore tunnel, but it’s only the end of the first chapter in the story of building Britain’s high-speed railway under the Chiltern Hills.
“Several years of intensive, world class engineering lie ahead of us to complete the tunnels’ four ventilation shafts plus headhouses; install the mechanical and electrical plant and machinery, slab track and overhead electrical wires before trains begin passing through at 200mph.”
Each TBM is operated by a crew of around 17, working in shifts to keep the machines running when required 24/7. They are supported by over 100 people on the surface, managing the logistics and maintaining the smooth progress of the tunnelling operation.
In total over 450 people have worked on the tunnels over the last three years, including a dedicated production team who made 112,000 precision-engineered, fibre-reinforced concrete tunnel wall segments on site at a purpose build temporary factory – and a team processing the spoil from the tunnels.
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