Central structure completed on HS2's 1.4 km Wendover green tunnel

Construction of HS2's Wendover green tunnel has reached a major milestone with the two halves of the 1.4 km cut-and-cover structure now joined, completing the central section of the tunnel less than 18 months after installation of the first precast segment.

The tunnel is being constructed within a deep cutting alongside the A413, west of Wendover, by EKFB, HS2's main works contractor for the central section of the route through Buckinghamshire and into South Warwickshire and a joint venture of Eiffage, Kier, Ferrovial Construction and Bam Nuttall. Unlike a conventional bored tunnel, the structure is assembled in the open excavation before being progressively covered with excavated material and landscaped. Once complete, the railway will be largely hidden beneath the restored ground surface, reducing noise and visual impact for the surrounding area.

The structure has an unusual M-shaped cross-section that separates northbound and southbound trains. In total, the completed tunnel will incorporate approximately 2,740 precast concrete segments. Construction was divided into two advancing sections so excavation, foundation preparation, segment installation and backfilling could take place simultaneously at different locations. The two construction fronts finally met when the last segment of the central structure was installed in early October.

More than 1.2 million cubic metres of material, predominantly chalk, was excavated to create the tunnel cutting and level formation. Rather than removing this material from the site, much of it has been retained for reuse. As sections of the tunnel are completed, the chalk is being carefully placed and compacted around and above the structure, with the backfill sequence controlled so that loading is distributed evenly across the tunnel.

The restricted section beneath the temporary Ellesborough Road bridge required a different installation method. Most precast elements could be placed using conventional cranes, but the limited clearance beneath the bridge ruled that out. A self-propelled modular transporter supported on 16 sets of wheels was therefore used to lift and position the heavy concrete elements from below, allowing installation to continue without removing the temporary crossing.

With the main central structure connected, work is now shifting toward the portals at each end, completion of the floor slab and internal fitout. Ellesborough Road currently crosses the construction site on a temporary bridge and will ultimately be realigned over the completed tunnel before final landscaping restores the surrounding ground.

Wendover is one of five shallow green tunnels on the route between London and Birmingham, alongside Chipping Warden, Greatworth, Burton Green and Copthall in Hillingdon, which was completed in the summer. Wendover is also one of three green tunnels being built by EKFB, with construction experience shared between those teams to improve reinforcement prefabrication, concrete delivery through the tunnels and the scale of backfilling machinery.

The milestone moves Wendover beyond its main structural assembly phase, but substantial work remains before the railway disappears beneath the reconstructed landscape. Completing the portals, internal works, backfilling and road realignment will gradually transform what is currently a major open excavation into a buried section of the HS2 route.