HS2 has started construction of its first ‘green tunnel’, designed to blend the high speed railway into the landscape.

The one-and-a-half mile structure is being built at Chipping Warden in Northamptonshire and will reduce disruption for communities.

Unlike a normal underground tunnel, the design is being built on the surface using an off-site manufacturing approach to speed up construction and improve efficiency.

More than 5,000 giant concrete tunnel segments, made at a factory in Derbyshire, will be assembled on site. 

Once complete the tunnel will be covered by earth, covered with trees and shrubs and fit in with the surrounding countryside

Chipping Warden is one of five ‘green tunnels’ that are being built on phase one of the HS2 project, which is designed to improve links between London, Birmingham and the North, help level-up the economy and provide a low carbon alternative to car and air travel.

Applying lessons from the construction of the latest French high speed lines, the off-site approach was developed by HS2’s main works contractor, EKFB - a team made up of Eiffage, Kier, Ferrovial Construction and BAM Nuttall. 

The tunnel segments are being made by Stanton Precast in Ilkeston, Derbyshire as part of a contract which is set to create up to 100 local jobs.

Designed as an m-shaped double arch, the tunnel will have separate halves for southbound and northbound trains – each one the height of two double-decker buses. The tunnel will be built in sections, with construction expected to be complete in 2024.

HS2 Ltd’s 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 off-site manufacturing techniques being used will help cutting 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.”

Instead of casting the whole tunnel 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 5,020 segments will be steel reinforced, with the largest weighing up to 43 tonnes.

By reducing the amount of concrete and steel 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.

EKFB’s project manager, Jeremie Martin, said the HS2 green tunnels are “a first of its kind in the UK”.

“Seeing the first set of precast units being installed is a milestone that the whole team is very proud of,” he added. “This three-year construction programme will benefit from off-site manufacturing making the green tunnel build more efficient than the traditional on-site building method.”

A relief road has also recently been completed, which will take HS2 vehicles – and other local traffic – away from the centre of the village of Chipping Warden. This will later be extended, to take the A361 over the top of the green tunnel.

Similar green tunnels will also be built at nearby Greatworth as well as Wendover in Buckinghamshire and Burton Green in Warwickshire, stretching for a combined total of more than four miles.