Construction has started on HS2’s longest ‘green tunnel’, which is designed to merge the high-speed railway into the rural landscape and reduce disruption for the surrounding communities.

Unlike a bored tunnel, the tunnel is being built using a ‘cut and cover’ process by excavating a cutting, building the tunnel, burying it, and planting trees, shrubs, and hedgerows on top to blend in with the surrounding countryside.

The tunnel is located near Greatworth in West Northamptonshire and will be constructed from over 5,000 giant pre-case concrete segments, made at a specialist factory in Derbyshire. HS2’s main works contractor, EKFB, a consortium of Eiffage, Kier, Ferrovial Construction and BAM Nuttall, will assemble them on-site.

EKFB are applying lessons learned from building the latest French high-speed lines, opting for a modular approach instead of pouring concrete on site, which boosts efficiency and cuts the amount of the structure’s embedded carbon. All 5,410 segments tunnel segments, which are being made by Stanton Precast at Ilkeston in Derbyshire, will be steel reinforced, with the largest weighing up to 43 tonnes.

Greatworth is one of five ‘green tunnels’ in phase one of the HS2 project, and is designed as an m-shaped double arch with separate halves for southbound and northbound trains. The double arch is the height of two double-decker buses and is built from five concrete precast segments that are slotted together one central pier, two side walls, and two roof slabs.

The tunnel will be built in sections, with the main structure expected to take around two years to build, and will require realignment of some local roads and footpaths. Landscaping will include thousands of native trees and shrubs including Silver Birch, Oak, Beech, and Willow to create new woodland areas around the portals and recreate hedgerows and field boundaries on top of the tunnel.

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.”

EKFB’s Programme Director Emmanuel Rossignol, said: “To see the construction start on HS2’s second cut and cover tunnel in Northamptonshire is a proud milestone for the team. The design and construction approach of this tunnel is unique to the UK, and there are many benefits associated with this methodology, including a reduction in our carbon footprint, but it’s not been without its challenges along the way.

“Our expert teams are to thank for their dedication as we continue to advance the construction programme across the Chipping Warden and Greatworth green tunnels.”