HS2 has released new images for the longest “green tunnel” its teams will be building across Buckinghamshire and Northamptonshire.
The design of the three tunnels is intended to help the infrastructure blend seamlessly with the surroundings.
The longest is the one-and-a-half-mile long Greatworth tunnel. This will be built at a factory in Derbyshire and then shipped over to be assembled on the railway line in Northamptonshire. The structure will then be covered with earth and landscaped to fit the character of the surrounding countryside.
This ‘off site’ modular approach was developed by HS2’s main works contractor, EKFB — a joint venture comprising Eiffage, Kier, Ferrovial Construction and BAM Nuttall. To develop the strategy, it applied lessons from the construction of modern French high-speed lines.
Designed as an ‘m’ shaped double arch, the tunnel 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 — one central pier, two side walls and two roof slabs. All 5,400 segments installed at Greatworth will be steel-reinforced, with the largest weighing as much as 43 tonnes.
The lighter-weight modular approach is also intended to half the amount of carbon embedded in the structure, as it uses less materials – concrete and steel being known as large sources of carbon emissions. The methodology also requires fewer people and equipment on site, improving safety and reducing disruption for residents.
HS2 Ltd’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.”
EKFB delivery director, Andy Swift, said: “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.”
Similar structures will also be built near Wendover in Buckinghamshire and Chipping Warden in Northamptonshire, stretching a combined total of four miles. The tunnels will all 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.
Teams will excavate thousands of tonnes of rock and earth during the initial stages of construction. These will be carefully separated and stockpiled on site for reuse later in the process, helping to keep trucks off local roads.
Individual landscaping plans will be developed for each tunnel. These will include thousands of native trees and shrubs typical to the local area, such as silver birch, oak, beech and willow to create new woodland areas around the portals and recreate the hedgerows and field boundaries on top of the tunnel.
All 13,290 segments belonging to the three tunnels are being made by Derbyshire-based Stanton Precast Ltd, in a deal that has created almost 100 jobs at their Ilkeston factory. Stanton currently employs about 180 people at their factory – and this deal has enabled the firm to increase their workforce by around 50%. New production sheds, casting and storage areas are also being built at the factory to accommodate the new work.
