Massive concrete box ready for A46 slide
Construction of a 14,500-tonne concrete box that will carry HS2 under the A46 Kenilworth Bypass has reached a key milestone with the installation of 120 beams.
Each beam, measuring between 13 and 24m in length, was lifted into place by three cranes to form the structure’s top. The operation, completed in just 14 days, was finished ahead of schedule by a dedicated team of engineers.
The box is being built next to the A46, rather than under the existing carriageway, to avoid up to two years of traffic management measures. With the beams now in place, the focus turns to completing the deck – the flat surface above the beams – and installing parapets.
In spring, the box will be pushed into its final position under the carriageway using a jacking mechanism developed by civil engineering firm Freyssinet. This method will push the box across a guiding raft at a rate of up to 2.5m per hour, covering a total distance of 64m.
The project involves close collaboration between HS2, National Highways, and construction partner Balfour Beatty VINCI (BBV). Two weekend closures of the A46 are planned in February to prepare for the box push. These closures will also allow road safety barriers to be upgraded, the central reservation layout adjusted, and drainage works completed.
A full closure of the A46 bypass is scheduled for spring 2025 and will last up to three weeks while the structure is moved into place.
Vicki Lee, senior project manager at HS2, acknowledged the team’s work so far: “I’d like to congratulate the entire site team for successfully moving such a large number of beams into place. I also thank motorists for their patience as we prepare for the box push in spring.”
John McNiffe, project director at BBV, added: “The safe and successful installation of 120 giant beams is a great achievement for our team. This phase required significant planning and precision, and I’m proud of how we’ve tackled it.”
The box’s design was developed by BBV’s design joint venture of Mott MacDonald and SYSTRA. Tim Akers, engineering manager at the joint venture, explained: “By building the structure off-site and using a rapid installation method, we’ve minimised the impact on road users and prioritised safety.”
When completed later this year, the box will enable HS2 trains to pass beneath the A46, part of the high-speed line connecting London and the West Midlands.