HS2 has revealed the first images of innovative ‘green tunnels’ that will be built across Buckinghamshire and Northamptonshire, which will blend the new HS2 rail line into the natural landscape
The one-and-a-half-mile-long Greatworth green tunnel will be built in a factory in Derbyshire before being shipped to site, and assembled over the railway line as it passes the village.
The tunnel will then be covered with earth and landscaped to fit into the surrounding countryside.
Applying lessons from the construction of the latest French high-speed lines, an ‘off site’ modular approach was developed by HS2’s main works contractor, EKFB – a team made up of Eiffage, Kier, Ferrovial Construction, and BAM Nuttall.
The tunnel has been designed as an ‘m’ shaped double arch, and will have two separate halves for southbound and northbound trains.
Instead of the whole tunnel being cast on site, five different concrete precast segments will be slotted together to achieve the double arch.
All 5,400 segments installed at Greatworth will be steel-reinforced, with the largest weighing up to 43 tonnes.
As concrete and steel are some of the biggest sources of carbon emissions within the construction industry, HS2 have reduced the amount of materials needed for the tunnel.
This lighter-weight modular approach is expected to more than halve the amount of carbon embedded in the structure. It also requires less people and equipment on-site, improving safety and reducing disruption for residents.
‘Improving efficiency and safety’
HS2’s project client Rohan Perin, said: “The Greatworth green tunnel is a great example of what we’re doing to blend the new railway into the landscape and protect communities living close to the line.
“By adopting an ‘off site’ approach to manufacturing, we’re also cutting embedded carbon from the design, improving efficiency, safety and making the whole construction process less disruptive for the community.”
‘A green space which will blend into the surrounding landscape’
EKFB delivery director Andy Swift, also commented: “The green tunnel design is a combination of innovation, international engineering expertise, and thoughtful landscaping for its local communities to enjoy.
“Once the tunnels have been built, the original earth removed from the cutting to make way for the tunnel, will be repositioned, creating a green space which will blend into the surrounding landscape.”
All tunnels will have specially designed ‘porous portals’ at either end to reduce the noise of trains entering and exiting the tunnel and small portal buildings to house safety and electrical equipment.
Thousands of tonnes of rock and earth will be excavated during the initial stages of construction and will be carefully separated and stockpiled on-site for reuse later in the process, helping to keep trucks off local roads.
Tailored landscaping design plans will be developed for each tunnel, with thousands of native trees and shrubs typical to the local area to create new woodland areas around the portals and recreate the hedgerows and field boundaries on top of the tunnel.