HS2 has begun assembling the project’s longest ‘green tunnel’, which will be covered by earth, trees and shrubs in a bid to help it blend in with the Northamptonshire countryside.
The 2.7km Greatworth Tunnel is being built using a ‘cut and cover’ process, which involves excavating a cutting, building the tunnel and then burying it.
The tunnel structure will be made from more than five thousand giant concrete segments made at a specialist pre-cast factory in Derbyshire and then assembled on-site by EKFB, HS2’s main works contractor.
The modular approach to building the tunnel was taken instead of a traditional process of pouring the concrete on-site in order to boost efficiency and cut the amount of embedded carbon in the structure.
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 5,410 segments will be steel-reinforced, with the largest weighing up to 43 tonnes.
Greatworth is one of five ‘green tunnels’ that are being built as part of phase one of the HS2 project, which is designed to improve links between London, Birmingham and the north.
HS2 was given the go-ahead in 2020, despite a decade of sharply rising costs and repeated delays to the original project timeframe. The cost of completing the project has ballooned from £33bn a decade ago to an estimated £100bn today.
Earlier this year, a revamp of Euston station was delayed by two years due to “wildly unrealistic” budgeting. HS2 trains were originally scheduled to run in 2026, but they are now not expected to run into Euston until 2041 at the earliest.
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 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.”
Concrete and steel are some of the biggest sources of carbon emissions within the construction industry. By reducing the amount of both materials needed for the tunnel, this lighter-weight modular approach is expected to more than halve the amount of carbon embedded in the structure.
