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 鈥� negating the need to transport it elsewhere by road in an operation that would have resulted in around 100,000 truck movements.
It is the only 鈥榮ingle bore鈥� tunnel on the new high-speed line and its cavernous size is engineered to accommodate the forces generated by 200mph passing trains.
The tunnel is built by SCS 鈥� HS2鈥檚 main civil engineering contractor for the route鈥檚 southern section 鈥� which is made up of Skanska, Costain and Strabag.
Copthall is the first of five cut-and-cover tunnels to be completed on the HS2 route between London and the West Midlands 鈥� 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.
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.