Key Takeaways
- The 17-hour operation to install the 315-metre East deck of the M6 South viaduct was a success, marking a major milestone in the HS2 project.
- The "fully restrained" technique used to slide the viaduct into place allowed for minimal disruption to traffic, with only the M42 slip closed during the weekend.
- The operation was the first of its kind on a UK motorway, and it is expected to reduce the number of motorway closures needed to complete the project.
- The M6 South viaduct is designed to carry high-speed trains heading to Birmingham and further north, and its construction is a crucial part of the HS2 project.
- The project has reached the halfway point, with the same process to be repeated over the next year to install the parallel West deck.
Introduction to the M6 South Viaduct Project
The recent 17-hour operation to install the 315-metre East deck of the M6 South viaduct was the culmination of an epic three-stage process to assemble and install the structure. The operation was a major milestone in the HS2 project, which aims to connect London to Birmingham and other parts of the UK with high-speed trains. The M6 South viaduct is a critical part of the project, and its construction has required innovative solutions to minimize disruption to traffic and ensure the safety of workers and motorists.
The "Fully Restrained" Technique
The team behind the project, led by HS2’s main work contractor Balfour Beatty VINCI (BBV), worked closely with National Highways to develop a "fully restrained" process that allowed them to safely slide the final section of the viaduct above moving traffic. This technique, which is believed to be a first for a UK motorway, involved closing the M6 overnight between Junctions 4 and 5 to shift the viaduct slightly forward by twelve metres. This ensured that both ends of the enormous beam were fully supported on concrete piers during the slide. The viaduct was then pushed the rest of the way across the busy motorway on Saturday at a speed of 13 metres per hour, with only the M42 slip closed during the weekend.
The Benefits of the "Fully Restrained" Technique
The successful operation means that the project to construct the M6 South viaduct has reached the halfway point, and the same process will be repeated over the next year to install the parallel West deck. The "fully restrained" technique used in the operation has several benefits, including minimizing disruption to traffic and reducing the number of motorway closures needed to complete the project. According to Caroline Warrington, HS2 Ltd’s Head of Delivery, the technique has cut in half the number of times the motorway has had to be closed, making it a significant achievement for the project.
The Design and Construction of the M6 South Viaduct
The M6 South viaduct has been designed in stages to increase efficiency and reduce disruption for motorists. Each section is assembled to one side before being pushed out over the motorway, with the next section added behind it. The viaduct is formed of a hollow double-box structure made of weathering steel, which boasts a natural protective layer of oxidisation that gives it a characteristic "rusty" appearance and reduces maintenance by eliminating the need for regular repainting. The structural design of the viaduct has been carried out by Balfour Beatty VINCI’s Design Joint Venture (DJV), made up of Mott MacDonald and SYSTRA, plus WW+P Architects.
The Next Steps in the Project
The successful installation of the East deck viaduct marks a major milestone in the HS2 project, and the team is now focused on the next phase of the project. The neighbouring West deck viaduct will be launched in multiple phases throughout 2026, and the East deck finishing works will also be completed. The project has been designed to minimize disruption to traffic and ensure the safety of workers and motorists, and the use of innovative techniques such as the "fully restrained" method has been crucial to its success. As Mark Wild, HS2 Ltd’s Chief Executive, noted, the project is focused on safely boosting levels of productivity across the construction programme, and the M6 South viaduct is a critical part of this effort.
Conclusion
The successful installation of the East deck viaduct is a significant achievement for the HS2 project, and it marks a major milestone in the construction of the M6 South viaduct. The use of innovative techniques such as the "fully restrained" method has minimized disruption to traffic and ensured the safety of workers and motorists. As the project moves forward, the team will continue to focus on safely boosting levels of productivity across the construction programme, and the M6 South viaduct will play a critical role in the success of the HS2 project.
