The A361 road near Chipping Warden in Northamptonshire has reopened following completion of a major stage in the construction of a tunnel for the new HS2 railway line.

The 2.5 km-long tunnel is one of the longest ‘cut-and-cover’ tunnels on HS2, and is being built inside a cutting.

After completion, the earth is replaced to form a ‘green tunnel’ that blends the railway into the landscape, reducing noise and disturbance for nearby residents.

To enable the carriageway to be realigned over the top of the first section of the tunnel, a short section of the A361 between Banbury and Daventry was closed for 11 days, but was reopened last Friday, 3rd October.

Work will now start on constructing a missing section that will link up the two parts of the tunnel already built. Chipping Warden is being assembled from precast concrete segments, with separate halves for northbound and southbound trains.

Although the construction method originally chosen offered significant carbon savings, it resulted in significant productivity challenges. As a result, several improvements were made to the construction process, resulting in the rate of installation doubling from an average of two segments a day in 2022/23 to five-and-a-half per day this year.

Lessons learnt from constructing the Chipping Warden tunnel are also being used for similar tunnels at Wendover and Greatworth.

“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 the completion of the tunnel. “The improvements we’ve made to construction processes over the last year have helped us turn a corner – but we still need to keep up the focus on productivity, while delivering the work safely and to the necessary quality. I’d also like to thank our neighbours for their patience during the road closure, which was necessary to complete the realignment of the road and our site teams for working so hard to get it reopened on time.”

HS2 Ltd’s Senior Project Manager, Hugo Rebelo