TGV-style off-site techniques inspire HS2 tunnel designs

7 January 2022

HS2 will use lessons learnt from the construction of French high-speed lines (‘TGV’) to build around 7km of tunnels using an off-site modular approach.

Further developed by HS2’s main works contractor EKFB (Eiffage, Kier, Ferrovial and BAM Nuttall), the techniques will be applied initially to three tunnels at Greatworth and Chipping Warden, Northamptonshire, and Wendover, Buckinghamshire.

The methodology is a modern take on traditional cut-and-cover but rather than cast concrete or create other structures in situ, the tunnel components are made in the factory and assembled on site. Five separate precast reinforced concrete elements – a central pier, two lateral piers and two curved roof arches – will be ‘slotted’ together on site to create an M-shaped double-arched ‘ring’ with separate northbound and southbound tunnels.

A total of 5,400 factory-built elements will go to make the 2.4km-long Greatworth tunnel. The three tunnels will require a total of 13,290 elements which will be made by Stanton Precast in Derbyshire.

Once assembled, the tunnels will be backfilled and landscaped: excavated spoil will be stockpiled on site for reuse later in the process. Each tunnel will have new woodland areas above created by planting native trees and shrubs, including silver birch, oak, beech and willow. The tunnels will also have ‘porous’ portals to reduce noise levels as trains enter and exit.

“The green tunnel design is a combination of innovation, international engineering expertise and thoughtful landscaping for its local communities to enjoy,” said Andy Swift, EKFB Delivery Director. “Once the tunnels have been built, the original earth removed from the cutting to make way for the tunnel, will be repositioned, creating a green space which will blend into the surrounding landscape.”

Enhancing the scheme’s environmental credentials, the modular construction involves reduced amounts of concrete and steel which, according to HS2 Ltd “is expected to more than halve the amount of carbon embedded in the structure”…and “requires less people and equipment on site, improving safety and reducing disruption for residents.”