Rapid progress marked on 2.7 km HS2’s longest green tunnel

The next phase of HS2’s longest green tunnel advanced this week with the realignment of the B4525 near Greatworth, enabling excavation to continue along the 2.7-kilometre cut-and-cover structure. The tunnel is being built within a shallow cutting and will later be buried and landscaped to integrate the railway into the surrounding rural environment.

Engineers have already completed the first kilometre of the precast concrete “M-shaped” tunnel, which accommodates separate northbound and southbound tracks. Early challenges at the nearby Chipping Warden tunnel prompted HS2 Ltd and contractor EKFB to overhaul construction methods. These refinements now allow teams at both sites to install five to six precast segments per day, more than doubling initial output.

Improvements include introducing roll-mat reinforcement for quicker blinding, modifying concrete delivery routes, and using prefabricated reinforcement cages to speed up construction of the invert slab. Aerated concrete is now used to fill the central valley of the tunnel profile, offering a faster and more consistent solution. A dedicated test section at Chipping Warden allowed the team to trial these methods without affecting the programme.

The streamlined process reduces work-face congestion and mitigates schedule risks during winter construction. HS2 officials note that productivity gains have enabled road reopenings and will support continuous progress on the tunnel throughout the season.

Once complete, the Greatworth tunnel will form part of a network of five green tunnels designed to reduce surface impacts and improve connectivity between major UK cities while allowing more capacity on existing rail lines.