Construction of the first HS2 ‘green tunnel’, which will use reduced amounts of concrete and steel, began today in Northamptonshire.
The tunnel, which is located in Chipping Warden and will span 1.5 miles, is being built on phase one of the project and uses technology aimed at minimising disruption for communities.
Unlike conventional tunnels, which use boring machines, the green tunnels are being constructed at ground level using segments that will be joined and eventually covered in earth, trees and shrubs to blend in with the surrounding countryside.
The more than 5,000 giant concrete segments are being built offsite at a factory in Derby, which will help to speed up construction and improve efficiency.
The lighter-weight modular approach being used will more than halve the amount of cement and steel – two carbon-heavy materials – that is used. It also requires fewer people and less equipment on site.
Set for completion in 2024, the tunnel represents the start of another major piece of HS2 infrastructure, following the installation of the first segments of the Colne Valley viaduct last month.
Designed as an M-shaped double arch, the Chipping Warden tunnel will have separate halves for southbound and northbound trains – each one the height of two double-decker buses.
Instead of casting the whole tunnel on site, five concrete precast segments will be slotted together to achieve the double arch – one central pier, two side walls and two roof slabs.
All 5,020 segments will be steel-reinforced, with the largest weighing up to 43 tonnes.
Jeremie Martin, project manager of EKFB, HS2’s main contractor, celebrated the milestone and the efforts of the team.
He said: “This three-year construction programme will benefit from offsite manufacturing, making the green tunnel build more efficient than the traditional, on-site building method.
“The HS2 green tunnels are the first of their kind in the UK. We have designed them as a twin-arch M-shape, which is more efficient than the standard box structure, reducing the amount of concrete required, which is a great example of how innovative engineering design can reduce carbon impact.”
The green tunnels will have specially designed ‘porous portals’ at either end to reduce the noise of trains entering and exiting the tunnel, along with small portal buildings to house safety and electrical equipment.
Further tunnels will be constructed near Greatworth, also in Northamptonshire, in addition to Wendover (Buckinghamshire) and Burton Green (Warwickshire), stretching for a combined total of more than four miles.
HS2 project client Rohan Perin said: “The Chipping Warden green tunnel is a great example of what we’re doing to reduce disruption for people living close to the railway and it’s fantastic to see the first arches in position.
“Our trains will be powered by zero-carbon electricity, but it’s also important to reduce the amount of carbon embedded in construction. The offsite manufacturing techniques being used will help cut the overall amount of carbon-intensive concrete and steel in the tunnel, and make the whole process faster, more efficient and therefore less disruptive for the community.”