Work has started on HS2's longest 'green tunnel' in West Northants.

Unlike a bored tunnel, the shallow one-and-a-half mile (2.7km) tunnel is being built using a ‘cut and cover’ process. This involves excavating a cutting, building the tunnel and then burying it, with trees, shrubs and hedgerows planted on top to blend in with the surrounding countryside.

The tunnel structure will be made from more than 5,000 giant concrete segments, made at a specialist pre-cast factory in Derbyshire, and assembled on site by HS2’s main works contractor, EKFB - a team made up of Eiffage, Kier, Ferrovial Construction and BAM Nuttall.

Applying lessons from the construction of the latest French high-speed lines, EKFB opted for this modular approach - instead of a traditional process of pouring the concrete on site - to boost efficiency and cut the amount of embedded carbon in the structure.

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Greatworth 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, boost the economy and free up more space on the existing rail network for freight and local services.

HS2 Ltd's Project Client Neil Winterburn, said: "Greatworth is one of five green tunnels between London and Birmingham designed to protect the natural environment and reduce disruption for local communities - and it’s great 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 help spread the supply chain benefits of the project across the UK."

Designed as an m-shaped double arch, the tunnel will have separate halves for southbound and northbound trains. Five different concrete precast segments will be slotted together to achieve the double arch which is the height of two double-decker buses - one central pier, two side walls and two roof slabs.

The tunnel segments are being made by Stanton Precast in Ilkeston, Derbyshire, as part of a contract which could create up to 100 local jobs. All 5,410 segments will be steel reinforced, with the largest weighing up to 43 tonnes.