HS2 has completed the first finished cut-and-cover tunnel on Britain’s new high-speed railway, marking another major milestone as construction gathers pace across the 140-mile route between London and the West Midlands.
The 880-metre Copthall Green Tunnel, near West Ruislip, is the first of five cut-and-cover tunnels on the project to have both its concrete structure completed and its earth covering reinstated.
Built by Skanska Costain STRABAG (SCS), the tunnel forms part of HS2’s southern section between the Northolt tunnels and the Colne Valley Viaduct.
Originally designed as an open cutting, the scheme was redesigned as a cut-and-cover tunnel to make use of around 1.2 million cubic metres of excavated material generated during construction of the nearby Northolt twin-bore tunnels.
The approach avoided the need to remove the material by road, eliminating an estimated 100,000 HGV movements while reducing disruption to surrounding communities.
The tunnel is the only single-bore structure on the HS2 route and has been engineered to accommodate trains travelling at speeds of up to 200mph.
With the main civil engineering works now complete, the next phase will see trees, shrubs and other planting established above the structure to allow it to blend into the surrounding landscape.
The milestone comes as work continues across the other four cut-and-cover tunnels on the route, including Chipping Warden Tunnel in Northamptonshire, where the concrete structure was recently completed ahead of backfilling.
Rail Minister Lord Peter Hendy said: “The completion of Copthall tunnel marks another significant milestone for HS2. Making use of innovative design, the tunnel reduces the impact on nearby communities by blending into its surroundings whilst keeping thousands of truck journeys off local roads by using materials close to the site.
“Our reset of HS2 is driving faster, more efficient construction on-the-ground and supporting thousands of jobs as we work to deliver the project at the lowest reasonable cost.”
The project forms part of a broader acceleration in construction activity across HS2, with the programme now at peak delivery.
HS2 says six major construction milestones have been achieved ahead of schedule over the past year, while Chief Executive Mark Wild continues to lead a programme-wide reset aimed at improving productivity and reducing costs.
Earlier this year, the Department for Transport confirmed a revised delivery schedule and updated cost profile for the railway, alongside proposals to simplify elements of the scheme, including operating trains at speeds comparable with high-speed railways in Japan and mainland Europe. The changes are expected to reduce costs by up to £2.5 billion and shorten the construction programme by around a year.
James Leeming, Head of Delivery at HS2, said: “Finishing civil works on HS2’s first-completed ‘green’ tunnel clearly demonstrates the progress that’s being made to deliver the first new intercity railway north of London in over a century.
“I pay tribute to the dedicated workforce that has worked since early 2021, and in all weathers, to deliver this remarkable structure, which was a key component of our plan to deal with the muck excavated to build part of HS2’s tunnelled sections.”
Copthall Tunnel measures up to 16 metres wide and 12 metres high internally, with five natural ventilation shafts extending as much as 17 metres from the surface to the tunnel roof.
Engineers used travelling formwork and falsework systems capable of advancing 20 metres at a time, enabling the curved structure to be built efficiently while maintaining quality and safety.
The project also involved diverting and rebuilding Harvil Road and constructing a new bridge over the high-speed railway, alongside work adjacent to both the Chiltern Main Line and the Colne Valley Viaduct.
Jonathan Morris, Managing Director at Skanska Costain STRABAG, said: “Combining an ambitious tunnel design, engineering expertise, and high-quality construction, Copthall Tunnel is a fantastic example of how we are building the railway in harmony with the environment.
“Skanska Costain STRABAG joint venture has delivered this key part of HS2 thanks to great partnerships and a collaborative approach to every stage of construction. My thanks go out to the brilliant team who has delivered this milestone whilst maintaining the highest levels of safety throughout delivery.”
Over the next two years, landscaping and ecological planting will continue above the tunnel as the new landform is integrated into the surrounding countryside.
