HS2 has completed construction of its first cut-and-cover, ‘green’ tunnel, marking a further milestone in the delivery of Britain’s new high-speed railway between London and the West Midlands.
The 880-metre Copthall Tunnel, near West Ruislip in west London, has been constructed using approximately 1.2 million cubic metres of material excavated during the creation of the nearby twin-bore Northolt Tunnel.
Originally planned as an open cutting, the route was redesigned as a cut-and-cover tunnel. The change enabled excavated material from the Northolt Tunnel to be reused on site, avoiding an estimated 100,000 lorry journeys that would otherwise have been required to remove the spoil.
Copthall Tunnel is the first of five planned green tunnels on the HS2 route to be fully completed, with both the tunnel structure and the earth covering now in place. Landscaping work, including the planting of trees, shrubs and other vegetation, will continue over the next two years to integrate the structure into the surrounding environment.
The tunnel forms part of the southern section of the railway being delivered by the Skanska, Costain and STRABAG (SCS) joint venture.
Located between the Northolt Tunnel and the Colne Valley Viaduct, the structure is more than half a mile long, approximately 12 metres high and up to 16 metres wide internally. It has been designed to withstand the aerodynamic forces created by trains travelling at speeds of up to 200mph. Five ventilation shafts extend from the landscape above to the tunnel roof, reaching depths of up to 17 metres.
Construction involved the use of travelling formwork and falsework systems that advanced in 20-metre sections, allowing engineers to build the tunnel along its curved alignment.
The project also included the diversion and reconstruction of Harvil Road, alongside the construction of a new bridge carrying the road over the railway.
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.
The completion of Copthall Tunnel follows continued progress across the HS2 programme. The remaining four green tunnels are also under construction, with HS2 recently confirming that structural works on Chipping Warden Green Tunnel in Northamptonshire have been completed ahead of backfilling.
Once landscaping is complete, the tunnel will form part of a continuous green corridor across the site while carrying high-speed rail services beneath the restored ground level.
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.
HS2 has said the project is currently at its peak construction phase. Earlier this year, the UK Department for Transport confirmed a revised delivery schedule and updated cost estimates as part of an ongoing programme reset. The department also announced proposals to simplify parts of the railway by operating trains at speeds comparable with high-speed networks elsewhere in Europe and Japan, with the aim of reducing costs and shortening the construction programme.
