HS2 completes final tunnel segments on Chipping Warden Green Tunnel following major construction recovery

HS2 has reached a significant construction milestone with the installation of the final precast concrete segment at the Chipping Warden Green Tunnel in Northamptonshire, marking the completion of a key structural phase after earlier engineering challenges delayed the project.

The final section is the last of 5,020 reinforced concrete segments that make up the cut-and-cover tunnel, which has been designed to reduce the visual and environmental impact of the high-speed railway on the surrounding landscape.

The achievement follows a difficult period for the project after defects were identified in some of the precast concrete units in 2022, prompting a comprehensive review of construction methods and quality assurance processes.

Construction enters final fit-out phase

With the structural shell now complete, work will focus on finishing the tunnel's internal infrastructure.

Construction teams are progressing waterproofing works, casting the internal floor slab and installing emergency walkways that will run alongside the railway once the line enters service.

https://www.youtube.com/watch?v=MfQeeKW2WSQ

The tunnel was constructed using a two-stage approach, with crews building separate sections before connecting them together. The final segments were installed near the A361, completing the link between both halves of the structure.

Lessons learned improve productivity

The Chipping Warden Green Tunnel is one of three major green tunnels being delivered by EKFB—the joint venture comprising Eiffage, Kier, Ferrovial Construction and BAM Nuttall—along this section of the HS2 route.

Project leaders say the experience gained in overcoming the earlier construction issues has led to significant improvements in productivity and delivery methods.

Those lessons are now being applied to the construction of the Greatworth and Wendover green tunnels, which use similar precast construction techniques.

Chris Barrett, Senior Project Manager at EKFB, said the milestone reflected the team's ability to adapt following the setbacks experienced during the early stages of construction.

"Watching the final tunnel segment being lifted into place is the outcome of 18 months of rewriting the playbook, learning, innovating and putting the right solutions forward when challenged, all of which have boosted on-site productivity.

"This success has allowed EKFB to safely work at twice the speed compared with the start of construction works in 2023. Now our focus shifts to completing waterproofing and internal works as well as backfilling earth around the tunnel and, by the end of winter, it'll be buried and largely out of sight."

Designed to minimise environmental impact

Unlike conventional bored tunnels, green tunnels are constructed by excavating a trench before installing precast concrete sections and covering the structure with earth once complete.

The finished tunnel will blend into the surrounding countryside, reducing noise and visual intrusion while allowing the landscape above to be restored for agricultural use and wildlife habitats.

Progress continues despite earlier setbacks

The completion of the tunnel's structural shell represents an important step in the delivery of HS2's central section through Northamptonshire.

While the Chipping Warden Green Tunnel experienced well-publicised quality issues during construction, the project has since implemented revised manufacturing standards, enhanced quality controls and updated installation techniques.

As internal fit-out work continues and earthworks begin to restore the surrounding landscape, the project moves closer to completing one of the largest green tunnel structures on the HS2 network, demonstrating how lessons learned from early construction challenges are being applied across the wider programme.