Hünnebeck by BrandSafway and MPB Structures have been delivering formwork and concrete solutions for BBV (Balfour Beatty VINCI) and HS2 (High Speed 2) for the ground-breaking, 2600-tonne, Marston Box HS2 bridge job – the world’s longest box slide on a bridging project.

MPB built the massive bridge structure over a six-month period – right next to the M42 motorway in Warwickshire – with Hünnebeck providing the formwork and shoring solutions on this project described by HS2 as a “feat of engineering”.

The two big brand construction companies worked closely together, which enabled BBV to save time on the installation – significantly cutting costs and reducing the project’s carbon footprint, all of which minimised the impact on M42 motorists. After construction, the massive bridge was slid on liquid bentonite (a record) 165m into position by a 450-strong team on 29 December 2022 – using an innovative high-tech box jacking raft, designed by specialist civil and structural engineering company Freyssinet. The BBV team worked 24/7 to shift HS2’s Marston Box bridge into place over 40 hours (seven hours faster than target), at a speed of 4m/hour.

This is the first time this raft-based infrastructure technology has been used in the UK for a motorway bridge structure. And this high engineering construction method – allowing the structure to be shifted in situ in one movement – radically reduced traffic disruption on the M42 below, with only two one-week closures of the motorway over a 12-month period. Traditional bridging methods would have meant three months of total overnight closures and around two years of reduced lane widths and 50mph speed limits.

Mark Draycott, national infrastructure manager for Hünnebeck, says, “As the bridge structure was reduced in size, we worked together with MPB to provide the best solution for forming the structure. Often bridge structures like this are formed using ‘traditional formwork,’ which is labour- and material-intensive, but provides flexibility when forming complex structures. To increase efficiency on this project, our engineering teams collaborated perfectly, and a combination of our MANTO panel system and GASS shoring system was used on site to brilliant effect.

“It was essential to have early conversations to plan in tie holes that allow the system to be held together through the reinforcement, accurately design the solution and carefully plan its installation on site. Due to the careful planning and agreement from BBV, Hünnebeck provided the formwork and shoring systems to MPB Structures to build Marston Box. We were well positioned from a logistics capability, as our main base is only two miles from the site, which also significantly reduced the amount of transport to the site as well as carbon emissions.”

Sasan Ghavami, Balfour Beatty VINCI’s construction director for the project, says, “We’re extremely proud to have successfully delivered the world’s longest box slide. It’s a huge achievement for our project team and everyone connected with Balfour Beatty VINCI. We’ve used innovative construction techniques and worked tirelessly throughout the Christmas period to move this 12,600-tonne bridge over the M42 motorway – all done with the aim of keeping disruption to an absolute minimum.”

Marston Box will connect to Dunton Wood Embankment to the south and with the Birmingham and Fazeley Canal Viaduct, which crosses the canal, to the north. The completed structure will be approximately 190m in length, of which approximately 82m is the Marston Box structure itself.