HS2 engineers have completed a 17-hour-long operation to slide a 4,600-tonne viaduct across the M6, without closing the motorway.
While a previous slide required a weekend closure of the main carriageway, the team – led by HS2’s main work contractor Balfour Beatty Vinci (BBV) – worked with National Highways to develop a new ‘fully restrained’ process. This allowed the final section to be slid into place above the moving traffic.
The team undertook 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.
As part of the procedure, the M6 was initially closed overnight between Junctions 4 and 5 on 11 December to shift the viaduct forward by 12m. This allowed the team to ensure both ends of the beam were fully supported on concrete piers during the slide.
With the slide completed, the project to construct the M6 South viaduct has reached the halfway mark.
Next year, the same process will be repeated, with a parallel west deck slid into position alongside the first to carry trains heading south.
Caroline Warrington, HS2 Ltd’s head of delivery, said: “Along the HS2 route, we are pioneering new approaches to engineering and construction 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.”
Comprehensive programme reset
Following a series of delays across the project, HS2 Ltd’s chief executive Mark Wild is currently leading a comprehensive reset of the programme.
As part of the focus on improving productivity and efficiency, while also reducing disruption for motorists, the M6 South viaduct has been designed in stages. Each section is assembled to one side before being pushed out over the motorway, with the next section added behind it.
In the latest phase, the team moved the viaduct using a series of strand jacks. To reduce friction, the structure was slid across non-stick pads, using a material usually found on the surface of household frying pans.
Russell Luckhurst, 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.”
Victoria Lazenby, National Highways’ regional director for the Midlands, added: “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.“
Shows what you can do when you try… and money is no object. The lack of disruption to the traffic flow on the roads below is a marked contrast to the deliberate obstructions that have been in place on the M6 at Penrith – Clifton/Lowther – for some time, and the closures planned when that WCML rail bridge – not obviously defective and only 58 years old – is replaced.