A 315-metre bridge deck that will carry HS2 trains was slid over the M6 motorway in a 17-hour operation on Saturday 13th December without closing the road to traffic below.
It was the third and final slide in a three-stage process to assemble and install the east deck of the M6 South viaduct.
While the previous deck slide had required a weekend closure of the main carriageway, the team 鈥� led by HS2鈥檚 main work contractor Balfour Beatty Vinci (BBV) 鈥� worked with National Highways to develop the 鈥榝ully restrained鈥� process that allowed them 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.
The contractors, they initially closed the M6 overnight between Junctions 4 and 5 on Thursday 11th December to shift the viaduct slightly forward by 12 metres. This was to ensure that both ends of the beam were fully supported on concrete piers during the main 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 operation means the project to construct the M6 South viaduct has now 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.
Caroline Warrington, HS2 Ltd鈥檚 head of delivery, said: 鈥淎long 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.
鈥淲e believe this fully restrained slide was a first for the country, but most importantly it means we鈥檝e been able to cut in half the number of times we鈥檝e had to close the motorway. I鈥檇 like to thank everyone who worked so hard to make the operation a success.鈥�
The M6 South viaduct has been designed in stages, with each section 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 strand jacks with structure sitting on Teflon pads to reduce friction.
BBV project engineer Russell Luckhurst said: 鈥淲e鈥檙e 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.
鈥淯sing this 鈥榝ully restrained鈥� 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.鈥�
Each viaduct is formed of a hollow double-box structure made of weathering steel. The steel boasts a natural protective layer of oxidisation which gives it a characteristic 鈥榬usty鈥� appearance and reduces maintenance by eliminating the need for regular repainting.
Four pairs of concrete piers support the viaducts with the tallest one measuring 9.9 metres in height. A 4.5-metre-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 BBV鈥檚 design joint venture, made up of Mott MacDonald and Systra, with WW&P Architects.
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