Work begins on HS2’s longest green tunnel

The shallow 2.7km-long cut and cover tunnel is designed to blend the high-speed railway into the rural landscape and reduce disruption for communities around Greatworth in west Northamptonshire. EKFB, a team made up of Eiffage, Kier, Ferrovial Construction and BAM Nuttall, will excavate a cutting, build the tunnel and then bury it. Trees, shrubs and hedgerows will be planted on top to blend the tunnel into 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 EKFB.

Applying lessons from the construction of the latest French high-speed lines, EKFB opted for this modular approach, rather than the traditional process of pouring the concrete on site, to boost efficiency and reduce the amount of embedded carbon in the structure. This lighter-weight modular approach is expected to more than halve the amount of carbon embedded in the structure.

Greatworth is one of five ‘green tunnels’ being built on phase one of the HS2 project.

HS2 Ltd’s project client, Neil Winterburn, said it was important to reduce the amount of carbon embedded in the high-speed line’s construction.

“The off-site manufacturing techniques being used will help cut 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,” he said.

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 create the double arch.

The tunnel segments are being made by Stanton Precast in Ilkeston, Derbyshire. All 5,410 segments will be steel reinforced, with the largest weighing up to 43 tonnes.

The tunnel will be built in sections, with construction of the main structure expected to take around two years. Local roads and footpaths will be realigned to cross the tunnel.

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.

Shorter green tunnels are also being built at Wendover in Buckinghamshire, Burton Green in Warwickshire and in the London Borough of Hillingdon. 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.