The construction of one of the longest ‘cut-and-cover’ tunnels on the HS2 project has taken a major step forward with the opening of the realigned A361 over the top of the structure near Chipping Warden in West Northamptonshire.
Set to stretch for 2.5km, the shallow ‘green tunnel’ is being built inside a cutting, with the earth put back on top afterwards, helping to blend the railway into the landscape and cut noise and disturbance for people living nearby.
A short section of the A361, which runs from Banbury to Daventry, was closed for eleven days to allow the carriageway to be safely realigned over the top of the first section of the tunnel. This new section of the A361 joins the Chipping Warden Relief Road, which was completed by HS2 in 2022 to take traffic away from the centre of the village.
The reopening of the road on Friday means that HS2’s contractors can now begin work on the missing section that will link up the two parts of the tunnel they’ve built so far.
Assembled from precast concrete segments, the tunnel is in an ‘M’ shape, with separate halves for northbound and southbound trains. Inspired by similar structures on the French high-speed network, the precast approach was chosen because it promised to be quick to assemble, with much of the work done offsite.
However, while the thinner segments do offer significant carbon savings, the initial construction schedule proved overly optimistic, with the team facing significant productivity challenges during the first two years on site.
Recognising the need to change direction, the HS2 team worked closely with their main works contractor EKFB – a team made up of Eiffage, Kier, Ferrovial Construction and Bam Nuttall – to identify and put in place a series of improvements to the construction process.
As a result, the rate of installation has doubled from an average of two segments a day in 2022/23 to five-and-a-half per day this year, with 2.1km worth of segments now installed.
HS2 Ltd’s 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 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.”
Chipping Warden is one of five green tunnels on the HS2 project, so called because the cut-and-cover tunnels are landscaped on top and designed to blend into the countryside.
