Two parallel viaducts that will carry HS2 trains over the M6 near Birmingham airport have been completed.
The twin 320-metre-long M6 South viaducts are being assembled alongside the road and will be slid over the road over a series of weekends. Each section will be pushed out before later sections are added behind it.
The first viaduct to be built is the ‘East Deck’, which will carry two tracks taking trains towards London. The first section, which stretches for 119m, will be slid out over a slip road next to the motorway at the beginning of June.
The next stages, which take the viaduct over the motorway and the M6-M42 Link Road, will occur over two further weekend closures.
This complex process means the weight of the deck will increase with each push, up from an initial 1,300 tonnes to around 3,000 tonnes by the end of the year.
At this point, the railway will be on a slight gradient, so to help maintain control, the deck, which will eventually weigh around the same as 214 double-decker buses, is being pushed slightly uphill, with the finish point 4.2 metres higher than the start point.
Why is this an exciting phase?
Balfour Beatty VINCI’s Russell Luckhurst leads the team delivering these viaducts. He said: “We’re entering an exciting phase in the construction of these viaducts, as the first steel section begins to take shape. The assembly of these viaduct decks is taking place offline next to the motorway and is 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.”
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 is 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.”
Improving journeys
More than 200 major bridges and viaducts are being built as part of the HS2 project, which is designed to improve journeys between London, the West Midlands and the north, while freeing up space on the existing mainline for more freight and local services.
The complex operation led by Balfour Beatty VINCI is supported by the specialist steelwork company Victor Buyck Steel Construction (VBSC). The team is working closely with National Highways and drawing on recent experience of delivering the nearby M42/M6 link viaducts.
A series of winches, known as strand jacks, will be used to push the decks forward at a speed of between six and eight metres per hour, sliding across non-stick pads to reduce friction – a material usually found to the surface of a household frying pan.
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 slides will be needed to push this second viaduct across the road.
Both viaduct spans will be formed of a hollow double-box structure made of weathering steel. This kind of steel boasts a natural protective layer of oxidisation which gives it a characteristic ‘rusty’ appearance and reduces maintenance by eliminating the need for regular repainting.
Four pairs of concrete piers will support the viaducts with tallest one 9.9m in height. A 4.5m high parapet will be provided on the side facing the Chelmsey Wood to reduce noise and disturbance from passing trains.
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