By Ashley Karen
Together with subcontractor Kilnbridge, the Strabag, Skanska and Costain JV has finished the works on the HS2 Copthall cut and cover tunnel’s western portal, containing excavation and piling.
The Copthall Tunnel is located in the London Borough of Hillingdon and is one of five “green” – or cut and cover – tunnels on the High Speed 2 (HS2) route. The tunnel is 880m and will pose between the twin-bored Northolt Tunnel and the Colne Valley Viaduct.
HS2 Ltd.’s primary works civils contractor Skanska, Costain and Strabag JV (SCS), has been working on the Hillingdon site with the construction and engineering company, Kilnbridge.
First, before installing piles for the foundations of the tunnel structure, which will be built with a base slab, walls and a roof, the team bored nearly 20m down from the ground level.
Until now, along with a further 240m of walls for the tunnel, the team has completed the 110m western portal walls.
The tunnel is being built by employing reinforced concrete, and to make the roof of the box tunnel, a 40m m-long temporary deck will be set between the box walls, all supported by a moving gantry frame called a “roof traveller”.
The roof traveler and deck temporarily support the construction and pouring of the concrete roof. When the roof has achieved adequate strength, the roof traveler is lowered and moved along 20m to the next section of it, repeating the process.
To address materials shortages, HS2 Ltd. has set up a rebar treading facility at the Copthall construction site as well.
Harvil Road is being realigned and will travel over the western end of the new tunnel as part of the work in this area. Already, the deck for the road realignment has been installed, and the realigned Harvil Road is due to open in late 2023.
Malcolm Codling, HS2’s London tunnels client director, expressed: “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. approved that the tunnel construction between Old Oak Common and Euston station would be postponed, along with the commencement of Euston station and the northwest section of HS2 from Birmingham to Crewe (phase 2a).
James Richardson, SCS managing director, remarked: “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.”
As reported, HS2 will use the material excavated for the Copthall Tunnel – about 1.1M.m3 – to make sustainable wildlife habitats close to the tunnel, accordingly decreasing the spoil movement.
The “green tunnel” will be completed with trees, plants and shrubs on top.
After the last testing, the Balfour Beatty and Vinci JV’s (BBV’s) tunnelling team will launch the tunnel boring machine from the tunnel’s east portal. Over the last few months, sections of the TBM, comprising the 8.62m diameter cutterhead, were lowered into the TBM’s launch box, where it was assembled.
In partnership with tunnelling labor supply company Tunnelcraft, Balfour Beatty and Vinci JV was able to present multiple tunnelling operative apprenticeships for this phase of construction.
