How a 'UK first' has been achieved at HS2's Delta Junction viaduct

HS2 Ltd has completed the first viaduct section at the Delta Junction site in north Warwickshire, signifying a major milestone for the project.

The 472-metre-long single-track Tame West Viaduct is being built in a joint venture involving Balfour Beatty and Vinci (BBV).

Delta Junction itself forms a key part of the HS2 project, as the location where trains will veer off towards Curzon Street while also heading north towards Staffordshire. Once complete, the junction will form a triangle.

The completed viaduct section sits at the north of Delta Junction as HS2 crosses over the River Tame. Once complete, it will be one of three viaducts that will cross the river before converging at Curdworth Box.

In total, the River Tame West Viaducts will carry three tracks, the River Tame East Viaduct will carry a single track, and the Water Orton Viaducts two tracks.

Sam Hinkley, HS2’s Lead Senior Project Manager for Delta Junction, said: “Completion of the River Tame West single-track viaduct is a significant achievement for the Delta Junction team. This challenging area is home to some of the most complex engineering in the country.”

A technique which BBV believes to be a first in the UK has been used with this viaduct, and will also help in the construction of another nine viaducts at Delta Junction.

The viaduct section was erected using a mast and swivel crane that created a temporary deck, which will enable assembly of the segments. The crane lifts and installs one concrete segment into place at a time, eventually completing a 45-metre span length. Once in place, tensioning bars and cables are installed, fusing the segments together. This eventually means a cantilever is formed, and it is then tensioned permanently into place.

Stephane Ciccolini, site lead for BBV, told RAIL: “The idea was developed to help improve efficiency, and was perfect for here because it a complex site. We had to plan differently with how we were building the piers because we could not work in line, so it had to be a special way of constructing the pier and viaduct.”

Ciccolini explained that the viaduct construction for the River Tame West was also complicated because its location meant that the viaducts were converging, and thus the bridges were so close together.

“That is certainly a challenge, having them so close together. It adds complexities but we must overcome them. There are many innovations on this project, and it is based on the lessons learned from others. We’ve used all our collective experience,” he said.

The work began in 2023 with construction of the viaduct’s piers, with the concrete deck build-up commencing in early 2024.

Since then, a total of 190 pre-cast concrete segments, weighing 80 tonnes, have been successfully installed. The segments themselves have been built nearby at a factory in Kingsbury, before being moved to Water Orton.

Hinkley added that the geography of the site made the construction of Delta Junction much more difficult: “The different grades at the junction are difficult, but ensuring that we navigate the M6 motorway, other tracks and the landscape adds to the scale. We’re very pleased with the progress so far, though.”

In addition to the River Tame West Viaduct, the River Tame East Viaduct is also under construction nearby.

HS2 expects all deck segments to be in place in late 2026.