The construction of two parallel viaducts, which will carry HS2 trains over the M6 motorway near Birmingham Airport, has reached a significant milestone as the first section of structural steelwork is now complete.
In a move designed to minimise disruption for motorists, the twin 320-metre-long M6 South viaducts are being assembled off-site. They will then be carefully slid into place over the motorway during a series of weekend operations, with each section pushed out before subsequent sections are added behind them.
The ‘East Deck’, which will carry two tracks for trains travelling towards London, is the first viaduct to be built. Its initial 119-metre section is scheduled to be slid out over a slip road adjacent to the motorway during the weekend of 7th and 8th June.
Subsequent stages, which will see the viaduct extend over the main motorway carriageway and the M6-M42 Link Road, will take place over two further weekend closures. This intricate process means the weight of the deck will progressively increase with each push, growing from an initial 1,300 tonnes to approximately 3,000 tonnes by the end of the year.
The railway will be on a slight gradient at this point, so to help maintain control, the deck – which will eventually weigh roughly the same as 214 double-decker buses – is being pushed slightly uphill, with the finishing point 4.2 metres higher than its starting position.
Liam Kenney, HS2 Ltd’s Senior Project Manager, said: “It’s great to see the first section of the M6 viaducts coming together. The construction of these twin viaducts is a hugely complex process, and I’d like to thank everyone who has worked so hard to get us ready for the first slide.
“The multi-stage approach, learning lessons from previous bridge slides, will help reduce disruption for motorists and keep closures to a minimum.”
More than 200 major bridges and viaducts are being built as part of the HS2 project, which is designed to enhance journeys between London, the West Midlands, and the North, while simultaneously freeing up capacity on the existing mainline for more freight and local services.
The complex operation is being spearheaded by HS2’s main works contractor, BBV – a joint venture between Balfour Beatty and VINCI – with support from specialist steelwork company Victor Buyck Steel Construction (VBSC). The team is working closely with National Highways and drawing upon recent experience gained from delivering the nearby M42/M6 link viaducts.
A series of winches, known as strand jacks, will be employed to push the decks forward at a speed of between six and eight metres per hour. They will slide across non-stick pads to reduce friction – a material typically found on the surface of household frying pans.
The ‘West Deck’ – which will carry a further two tracks for northbound trains – will be assembled and slid out next year using the same technique. Due to the spacing of the piers, four separate slides will be required to manoeuvre this second viaduct across the road.
Russell Luckhurst, who leads the Balfour Beatty VINCI team delivering these viaducts, said: “We’re entering an exciting phase in the construction of these viaducts, as the first steel section begins to take shape. Assembly of these viaduct decks are taking place offline next to the motorway, and are being launched in a multi-phased approach, to reduce the impact on road users.
“The ‘East’ viaduct will be the first viaduct to be moved into place over three weekend closures, with the first launch taking place in June. The ‘West’ viaduct will be assembled and launched using the same method in 2026.”
Both viaduct spans will feature a hollow double-box structure made of weathering steel. This type of steel forms a natural protective layer of oxidisation, giving it a characteristic ‘rusty’ appearance and reducing maintenance by eliminating the need for regular repainting.
Four pairs of concrete piers will support the viaducts, with the tallest reaching 9.9 metres in height. A 4.5-metre-high parapet will be installed on the side facing Chelmsley Wood to mitigate noise and disturbance from passing trains.
