en.Wedoany.com Reported - The final precast concrete segment of the HS2 Chipping Warden cut-and-cover 'green tunnel' has been installed.
Engineers this week lifted the 5,020-tonne reinforced concrete segment into place, connecting the two independently built halves of the 2.5km tunnel near the A361 road.
The structure was built within an excavated cutting and will be backfilled and landscaped after completion, leaving the railway largely screened by earth, trees, and restored hedgerows. HS2's contractor says this approach reduces noise impact on nearby communities.
The main engineering contractor for the section is the joint venture EKFB, comprising Eiffage, Kier, Ferrovial Construction, and Bam Nuttall. EKFB has extensively used precast methods at Chipping Warden and the nearby Wendover and Greatworth tunnels to accelerate construction and reduce on-site labour requirements.
The joint venture said that during project delivery, the installation process was optimised, with rebar supplied in coils, prefabricated rebar cages and custom gantries introduced, and concrete delivery methods changed. EKFB stated that these improvements helped increase the average segment installation rate from approximately two per day in 2022/23 to about five and a half per day this year.
Chipping Warden is one of five planned 'green tunnels' between London and Birmingham, with others near Burton Green in Warwickshire and Copthall in the London suburbs nearing completion. The Chipping Warden structure features an M-shaped cross-section, with separate bores for northbound and southbound tracks.
With the precast wall installation complete, the site team is now focusing on waterproofing, pouring the internal base slab, and installing emergency access and other internal infrastructure in preparation for track installation. Over 2 million cubic metres of material, primarily mudstone, was excavated for the tunnel cutting, and this material is retained on site for backfilling and compacting the cutting before landscaping.
Backfilling speed has also been improved by using larger rollers, bulldozers, and dump trucks working above the structure, which were only permitted after safety tests to ensure the additional load would not endanger the tunnel below. The project team reports that, where possible, excavation, preparation, construction, and backfilling are carried out simultaneously at different points along the route to improve efficiency. The contractor said a test section of tunnel on site was used to trial new techniques before applying them to the permanent works.
The Chipping Warden works are part of the 225km London to Birmingham route of HS2 Phase One. HS2 Ltd Chief Executive Mark Wild is conducting a full review aimed at "redelivering the remaining route as efficiently and at the lowest reasonable cost." HS2 Ltd Senior Project Manager Sam Arrowsmith said it was great to see the final segment installed at Chipping Warden and thanked everyone who worked together to optimise every stage of construction. EKFB Senior Project Manager Chris Barrett said watching the final tunnel segment being lifted into place was the culmination of 18 months of rewriting the script, learning, innovating, and coming up with the right solutions when faced with challenges, all of which improved productivity on site.
