HS2’s ‘longest green tunnel’ now under construction in Northamptonshire

Construction has begun on the “longest green tunnel” of HS2, which runs through part of Northamptonshire.

The tunnel in Greatworth, near Brackley, will measure 2.7 kilometres and will use more than five thousand giant concrete segments when complete.

Greatworth is one of five ‘green tunnels’ that are being built on phase one of the HS2 project, which aims 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. Greatworth is the longest tunnel at a mile-and-a-half long.

According to the Government, the tunnels are designed to blend the high speed railway into the rural landscape and reduce disruption for communities around the railway line.

HS2 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.”

The 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.

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. All the tunnels will have specially designed ‘porous portals’ at either end to reduce the noise of trains entering and exiting the tunnel, along with small portal buildings to house safety and electrical equipment.

The tunnel will be built in sections, with construction of the main structure expected to take around two years. Local roads such as the B4525, Sulgrave Road, Helmsdon Road and access for Greatworth Park will be realigned to cross the tunnel, as well as local footpaths.

Tailored landscaping design plans are also being developed, with thousands of native trees and shrubs typical to the local area - such as Silver Birch, Oak, Beech and Willow - planted to create new woodland areas around the portals and recreate the hedgerows and field boundaries on top of the tunnel.

The team behind HS2 says lessons learned during the construction of a similar green tunnel at Chipping Warden are being applied to the delivery of Greatworth. These include changes to quality control and the delivery and installation of the segments.