Precast milestone as HS2 links Chipping Warden tunnel sections
The construction of HS2’s 2.5km Chipping Warden ‘green tunnel’ has reached a major milestone with the reopening of the A361 over its newly built section, allowing work to continue on linking both halves of the structure.
Located in West Northamptonshire, the tunnel is one of five shallow cut-and-cover tunnels being built for the high-speed railway. Once complete, it will carry trains beneath the landscape, reducing noise and visual impact for nearby communities.
Assembled entirely from precast concrete segments, the twin-bore structure forms an M-shape with separate tunnels for northbound and southbound trains. The precast approach—similar to those used on the French high-speed network—was selected for its speed, offsite efficiency and lower carbon footprint.
After initial delays, productivity has more than doubled, rising from two to over five tunnel segments installed per day, with 2.1km now complete. Improvements in logistics, reinforcement, and concrete pouring methods were first trialled on a dedicated test section before being applied across the site.
HS2 senior project manager Hugo Rebelo said: “We’ve had some serious challenges with the Chipping Warden green tunnel, so it’s great to see the A361 permanently diverted and a clear path ahead for completion. The improvements we’ve made to construction processes have helped us turn a corner — but we still need to keep up the focus on productivity, safety and quality.”
Each five-piece segment set is installed on a concrete base slab before being topped with aerated concrete fill, which replaces traditional aggregate. The use of prefabricated reinforcing cages and rolled mat steel has also accelerated construction.
EKFB project director Alexei Bond added: “The A361 road realignment marks the completion of a complex section of works. There’s still much to do, but unit installation is benefitting from increased productivity — a testament to the team’s hard work.”
The Chipping Warden tunnel is being delivered by EKFB, a joint venture between Eiffage, Kier, Ferrovial Construction and Bam Nuttall. Lessons from the project are informing the construction of similar precast green tunnels at Wendover and Greatworth.
Once operational, HS2 will halve journey times between London and Birmingham and free up capacity on the West Coast Main Line for local and freight services.
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