HS2 prepares for first M6 viaduct slide

The construction of two parallel viaducts that will carry HS2 trains over the M6 near Birmingham Airport has taken a major step forward, with the first section of structural steelwork now complete. To reduce disruption for motorists, the twin 320-metre-long M6 South viaducts are being assembled to one side and will be slid over the road over a series of weekends, with each section pushed out before later sections are added behind them.

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 119 m - will be slid out over a slip road next to the motorway during the weekend of 7/ 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 that 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 is being pushed slightly uphill, with the finish point 4.2 m higher than the start point.

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 is being led by HS2’s main works contractor, BBV – a team made up of Balfour Beatty and VINCI, supported by specialist steelwork company Victor Buyck Steel Construction (VBSC). The team are 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.

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. 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 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 4.5 m high parapet will be provided on the side facing the Chelmsey Wood to reduce noise and disturbance from passing trains.