Landmark HS2 operation moves massive viaduct across M6 without motorway closure

Engineers working on the HS2 project have completed what is believed to be a UK-first, successfully sliding a 4,600-tonne viaduct across the M6 motorway without closing the road to traffic, dramatically reducing disruption for drivers.

The 17-hour operation marked the final stage in a complex three-phase programme to assemble and install the 315-metre East deck of the M6 South viaduct. Once complete, the structure will carry high-speed trains travelling towards Birmingham and further north.

Earlier phases of the work had required full weekend closures of the motorway. This time, however, HS2’s main works contractor, Balfour Beatty VINCI (BBV), worked alongside National Highways to develop a new ‘fully restrained’ sliding technique. The approach allowed the massive structure to be moved safely over live traffic, a method thought to be unprecedented on a UK motorway.

To prepare for the main move, the M6 was closed overnight between junctions 4 and 5 on Thursday 11 December. During this closure, the viaduct was pushed forward by 12 metres so that both ends were fully supported by concrete piers ahead of the weekend operation.

On Saturday, engineers slid the viaduct the remainder of the way across the motorway at a steady speed of 13 metres per hour. Only the M42 slip road required closure, allowing traffic on the M6 to continue flowing throughout the operation.

The successful slide means construction of the M6 South viaduct has now reached its halfway point. Over the coming year, a parallel West deck will be assembled and moved into position using the same technique. This second structure will carry trains heading south.

The viaduct has been designed to minimise disruption by assembling sections beside the motorway before pushing them into place. Movement was achieved using powerful winches known as strand jacks, with the structure sliding across low-friction pads made from a material more commonly associated with non-stick cookware.

Each viaduct features a hollow double-box design made from weathering steel, which develops a protective oxidised surface that reduces long-term maintenance. The structures are supported by four pairs of concrete piers, the tallest standing 9.9 metres high. A 4.5-metre parapet will be added on the side facing Chelmsley Wood to reduce noise from passing trains.

The deck was launched with 82 precast slabs already installed, a move designed to further limit the number of future road closures required to complete the works. Structural design was carried out by Balfour Beatty VINCI’s Design Joint Venture, comprising Mott MacDonald, SYSTRA and WW+P Architects.

Russell Luckhurst, the BBV engineer leading the delivery of the works, said:

“We’re all feeling a huge sense of pride after sliding a 4,600-tonne viaduct into its final position this weekend. The third and final slide of the East deck viaduct was delivered over a live motorway for the first time in the UK, making this achievement even more special. Using this ‘fully restrained’ technique meant we were able to keep disruption to an absolute minimum. Our focus will now turn towards the neighbouring West deck viaduct, which will be launched in multiple phases throughout 2026, as well as the East deck finishing works.”

Caroline Warrington, HS2 Ltd’s Head of Delivery, said:

“Along the HS2 route we are pioneering new approaches to engineering and construction in order to deliver more efficiently and with less impact on our neighbours. We believe this fully restrained slide was a first for the country, but most importantly it means we’ve been able to cut in half the number of times we’ve had to close the motorway. I’d like to thank everyone who worked so hard to make the operation a success.”

National Highways Regional Director for the Midlands, Victoria Lazenby, said:

“Our key focus is the impact that these major construction works have on our roads – we must both ensure the safety of road users and minimise the disruption they face. So we are delighted that this innovative technique has meant that not only was this enormous structure slid into place without having to close the motorway during the day but also that the total number of closures needed has also been halved. We will continue to work with HS2 and their partners to ensure the smooth running of our roads while this huge infrastructure project takes place and support any initiatives which will reduce disruption for drivers and local communities.”

Image: HS2