HS2 green tunnel portal completed

Located in the London Borough of Hillingdon, the 880m-long tunnel structure sits between the twin bored Northolt Tunnel and the Colne Valley Viaduct.

Main works civils contractor SCS is completing the works with its sub-contractor Kilnbridge. So far, the western portal walls, spanning 110m, have been completed, along with a further 240m of walls for the tunnel.

The team initially excavated around 20m down from ground level, before installing piles for the foundations of the tunnel. The structure is then being constructed with a base slab, walls and a roof.

The tunnel is being built using reinforced concrete, allowing the trains to pass through and enabling green landscaping above. To create the roof of the box tunnel, a 40m-long temporary deck is positioned between the box walls, all supported by a moving gantry frame or ‘roof traveller’. The roof traveller and deck temporarily support the construction and pouring of the concrete roof. Once the roof has gained sufficient strength, the roof traveller is lowered and moved along 20m to the next section of roof.

As part of the works, Harvil Road is being realigned, and will travel over the western end of the Copthall Tunnel. The deck for the road realignment has already been installed and the realigned Harvil Road is due to open in late 2023.

The Copthall Tunnel is one of five green tunnels on the HS2 route. They are shallower tunnels that will be planted with vegetation on top to help them blend into the natural landscape. Materials from the excavation are kept on site and reused on the tunnel surroundings, reducing movement of spoil.