HS2 Ltd said close of work at two of the tunnel’s vent shafts at Chesham Road and Little Missenden brought to an end a project that began almost five years ago.
Trains travelling at 200mph will pass through the tunnel in just three minutes.
Align JV began main construction of the twin-bore tunnel in May 2021 with the staggered launch of two 2,000-tonne TBMs – Florence and Cecilia.
Five deep ventilation and access shafts were sunk to depths of up to 78m along its route and completed before the TBMs’ arrival.
The machines progressed north at an average speed of 16m per day before breaking through[https://www.tunnelsandtunnelling.com/news/final-breakthrough-made-on-hs2s-longest-tunnel/] near Great Missenden, Buckinghamshire, in early 2024.
Since then, work has continued to build the porous extensions[https://www.tunnelsandtunnelling.com/news/hs2-tunnel-portal-extensions-mitigate-sonic-boom-potential/] to the north and south portals, install internal walkways and fit out 40 cross-passages.
It is the second of HS2’s five twin-bore tunnels to be structurally complete. The 1.6km-long Long Itchington Wood Tunnel in Warwickshire was finished in February last year.
HS2 Ltd head of civil engineering for Chiltern Tunnel, Mark Clapp, praised everyone involved in the Chiltern Tunnel project.
“Multi-faceted projects of the Chiltern Tunnel’s scale and complexity don’t often come along; as a civil engineer, you’re lucky to be involved in anything like it. The team we assembled at HS2 Ltd, and with Align JV – our main civil works contractor – and all its subcontractors, to deliver this part of the new high-speed railway was exemplary,” said Clapp.
“I pay tribute to everyone involved. They can all feel certain that their hard work will stand the test of time.”
Align JV project director Adrien Baudard said being part of the successful delivery of the Chiltern Tunnel was a source of immense pride for everyone at Align and its supply chain partners.
“Their unwavering commitment, technical skill, and collaborative spirit have been truly impressive. Whether it was advancing safety standards, setting new TBM records, or helping to train future engineers, we’ve had the privilege of learning from and working with some of the top talent in our field,” said Baudard.
“With the completion of the Chiltern Tunnel’s civil works, the achievements of this integrated project team as well as the sustainable benefits such as carbon reduction and safety innovations will set a standard in tunnelling for generations to come.”
HS2 says the project team organised a sequenced operation to ensure the TBMs’ round-the-clock operation. Each installed 56,000 eight-tonne tunnel lining segments and together they excavated three million tonnes of chalk.
The excavated material has been used to create more than 120ha of chalk grasslands around the tunnel’s southern portal.
Completion of civil engineering works will be followed by the installation of mechanical, electrical and plumbing equipment, with the design-phase already under way and enabling works beginning this year. Rail systems, including track and overhead electrical equipment, will follow once this work is completed.
