HS2: SCS finishes excavation and piling on Hillingdon ‘green tunnel’ portal

The Copthall Tunnel, located in the London Borough of Hillingdon, is one of five “green” – or cut and cover – tunnels on the High Speed 2 (HS2) route. The 880m tunnel will sit between the twin bored Northolt Tunnel and the Colne Valley Viaduct.

HS2 Ltd main works civils contractor Skanska, Costain and Strabag joint venture (SCS) has been working on the Hillingdon site together with construction and engineering firm Kilnbridge.

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

The team has so far completed the 110m western portal walls, along with a further 240m of walls for the tunnel.

The tunnel is being constructed using reinforced concrete, and to create the roof of the box tunnel, a 40m long temporary deck will be positioned between the box walls, all supported by a moving gantry frame called a “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, repeating the process.

HS2 Ltd has also set up a rebar treading facility at the Copthall construction site to address materials shortages.

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

HS2’s London tunnels client director Malcolm Codling said: “The Copthall Tunnel is a vital part of the HS2 route in Hillingdon and once complete will blend into the local landscape as one of HS2’s green tunnels. Our London tunnels contractor SCS JV is making great progress in its construction, all part of the momentum of HS2’s delivery between Old Oak Common and Birmingham.”

Earlier this year, HS2 Ltd confirmed that construction of the tunnel between Old Oak Common and Euston station would be delayed, along with the opening of Euston station and the northwest section of HS2 from Birmingham to Crewe (phase 2a).

SCS managing director James Richardson commented: “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.”

HS2 will be using the material excavated for the Copthall Tunnel – approximately 1.1M.m³ – to create sustainable wildlife habitats near the tunnel, thus reducing the movement of spoil.

The “green tunnel” will be finished with tress, plants and shrubs on top.

HS2 CEO Mark Thurston and West Midlands mayor Andy Street with BBV apprentices and members of the tunnelling team

Elsewhere on the project, HS2 Ltd has published images of the tunnel boring machine (TBM) that will dig the scheme’s 5.6km Bromford Tunnel, running between Water Orton in North Warwickshire and Washwood Heath in Birmingham.

The 125m long, 1,600t TBM is called Mary Ann, the real name of famous author George Eliot, born in Nuneaton, North Warwickshire.

After final testing, the Balfour Beatty and Vinci joint venture’s (BBV’s) tunnelling team will launch the TBM from the east portal of the tunnel. Over the last few months, sections of the machine, including the 8.62m diameter cutterhead, were lowered into the TBM launch box where it was assembled.

BBV, in partnership with tunnelling labour supply company Tunnelcraft, was able to introduce multiple tunnelling operative apprenticeships for this phase of construction.