HS2 has reached a significant milestone with the completion of its first cut-and-cover “green” tunnel, marking visible progress on Britain’s new high-speed railway. The 880-metre Copthall tunnel, located near West Ruislip on London’s western edge, is the first of five such structures along the route between the capital and the West Midlands to be fully completed, including its earth covering.
Constructed using 1.2 million cubic metres of excavated material from the nearby twin-bore Northolt tunnel, the project highlights a growing emphasis on sustainable construction methods. Originally designed as an open cutting, engineers opted instead for a cut-and-cover solution, allowing all excavated material to remain on site. This innovation eliminated the need for roughly 100,000 lorry movements, significantly reducing disruption to local communities.
Engineering scale and design innovation
Copthall stands out as the only single-bore tunnel on the HS2 route, built to accommodate the aerodynamic forces generated by trains travelling at up to 200mph. Measuring more than half a mile in length, the tunnel reaches 12 metres in height and up to 16 metres in width internally, with ventilation shafts extending as deep as 17 metres from the landscaped surface above.
Delivery was led by SCS, the Skanska, Costain and STRABAG joint venture responsible for the southern section of HS2. The team adopted advanced travelling formwork and falsework systems, enabling construction to progress in 20-metre increments while maintaining the structure’s gentle curvature.
The tunnel also forms a key part of a complex section of the route, positioned between the Northolt tunnel and the Colne Valley viaduct—Britain’s longest railway bridge. Works in this area included the realignment and upgrade of Harvil Road, incorporating a new overbridge crossing the high-speed line.
Environmental integration and next phase
Now that civil engineering works are complete, attention turns to landscaping. Over the next two years, the tunnel will be covered with vegetation, including trees and shrubs, enabling it to blend seamlessly into its surroundings. This “green tunnel” approach is designed to mitigate visual and environmental impacts while supporting biodiversity.
Copthall is the first of five green tunnels to reach this stage, with others—such as the Chipping Warden tunnel in Northamptonshire—progressing rapidly.
Programme progress and project reset
The milestone comes amid a broader reset of the HS2 programme, led by HS2 Ltd CEO Mark Wild, aimed at improving efficiency and reducing overall costs. The 140-mile railway is now in peak construction, with productivity gains delivering several milestones ahead of schedule.
In May, the Department for Transport confirmed an updated delivery schedule and cost framework, alongside proposals to simplify the railway. This includes aligning train speeds with those used across Japan and mainland Europe, a move expected to save up to £2.5bn and shorten the construction timeline by approximately one year.
Industry reaction
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.”
James Leeming, Head of Delivery - 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.”
Jonathan Morris, Managing Director at SCS, added:
"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."
Image and video credits: HS2
