The HS2 high-speed rail project has reached a major milestone with the second tunnel boring machine (TBM), named Cecilia, completing its journey under the Chiltern Hills. This marks the end of an extensive 10-mile excavation, a process that began in June 2021 and took almost three years to complete. Cecilia's breakthrough at the tunnel's north portal follows closely on the heels of her twin sister machine, Florence, which arrived last month.
Together, Cecilia and Florence, each weighing 2,000 tonnes, cut the longest tunnel for the HS2 line, reaching depths of up to 80 meters and excavating three million cubic meters of chalk. These TBMs operated as underground factories, simultaneously excavating the tunnel and lining it with 56,000 precast concrete segments. This feat of engineering was achieved at an average rate of 16 meters per day.
The completion of the Chiltern tunnel is a crucial step for HS2, which promises to significantly reduce journey times between the UK's two largest cities with trains traveling at speeds of up to 200mph. The new line is also expected to reduce congestion on the West Coast Mainline, provide more capacity for local services, and almost double the rail capacity between London and the West Midlands.
The operation of each TBM required a dedicated crew of around 17 people per shift, supported by over 100 surface staff to ensure the seamless progress of this ambitious tunneling operation. Over 450 people have contributed to the completion of the tunnel over the last three years.
“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,” commented Mark Clapp, HS2 Ltd’s head of civil works for this section of the route.
