HS2 has revealed its first completed ‘green’ tunnel near West Ruislip, West London.

The 800 metre Copthall “cut and cover” tunnel has been created using 1.2 million cubic metres of material excavated during construction of the line’s nearby twin-bore Northolt tunnel.

Originally planned as an open cutting, engineers opted for a cut and cover design. The decision enabled the Northolt tunnel material to be kept on site – negating the need to transport it elsewhere by road in an operation that would have resulted in around 100,000 truck movements.

Copthall is the first of five cut-and-cover tunnels to be completed on the HS2 route between London and the West Midlands – meaning both the tunnel structure and the covering of earth over the top is finished. The next stage of works includes the planting of trees, plants, and shrubs on top to blend into the landscape.

It is the only single bore tunnel on the new high-speed line and is engineered to accommodate the forces generated by 200mph passing trains.

The tunnel is built by SCS – HS2’s main civil engineering contractor for the route’s southern section – which is made up of Skanska, Costain and STRABAG.

The other four green tunnels are also well advanced, with an announcement earlier in July that the structure of Chipping Warden tunnel in Northamptonshire has been completed ahead of works to backfill material.

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 is positioned between the twin-bore Northolt tunnel and the Colne Valley viaduct – Britain’s longest railway bridge, which was completed last year.

It is more than half a mile long, 12m high and up to 16m wide inside. Its five natural ventilation shafts reach down a maximum of 17metres to the tunnel’s roof from the newly-created landscape above.