Successful UK bridge slide

A technically challenging bridge slide has been carried out successfully in the UK as part of the HS2 project. This is the first time such a project has been carried out in the UK.

The engineering team managed to slide a 4,600tonne bridge section over the M6 motorway, without having to close the route to traffic, reducing disruption to drivers.

The 17 hour-long operation was the culmination of a three-stage process to assemble and install the 315m East deck of the M6 South viaduct, which will carry high-speed trains heading to Birmingham and further north . While the previous slide had required a weekend closure of the main carriageway, the team – led by HS2’s main work contractor Balfour Beatty VINCI (BBV)– worked closely with National Highways to develop the  process which allowed the team to safely slide the final section above the moving traffic. It is thought to be the first time this technique has been used on a UK motorway.

To deliver this, they initially closed the M6 overnight between Junctions 4 and 5 on Thursday 11 December to shift the viaduct slightly forward by 12m. This was to ensure that both ends of the enormous beam were fully supported on concrete piers during this weekend’s slide. The viaduct was then pushed the rest of the way across the busy motorway on Saturday at a speed of 13m/hour, with only the M42 slip closed during the weekend.

The successful operation means the project to construct the M6 South viaduct has reached the halfway point. Over the next year, the same process will be repeated, with a parallel West deck slid into position alongside the first one to carry trains heading south. Each viaduct is formed of a hollow double-box structure made of weathering steel. The steel features a natural protective layer of oxidisation which gives it a characteristic rust’ appearance and reduces maintenance by eliminating the need for regular repainting.

Four pairs of concrete piers support the viaducts with the tallest one measuring 9.9m in height. A 4.5m-high parapet will be installed on the side facing Chelmsley Wood to reduce noise and disturbance from passing trains. The viaduct was launched with 82 precast slabs already installed on top of the steel structure. This will further reduce the number of road closures in the future, to complete the viaduct deck works.

The structural design has been carried out by Balfour Beatty VINCI’s Design Joint Venture (DJV), made up of Mott MacDonald and SYSTRA, plus WW+P Architects.