Significant progress has been made in constructing two parallel viaducts to carry HS2 trains over the M6 motorway near Birmingham Airport, following the completion of the first section of structural steelwork.

Disruption to motorway users is being kept to a minimum by assembling the twin 320-metre-long viaducts at one side of the M6, then sliding them into place over a series of weekends, each section being pushed out before adding more sections behind them.

The first viaduct, the ‘East Deck’, will carry two tracks for trains towards London. The first section, 119m long, will be slid out over a motorway slip road during the weekend of 7th/8th June, with the next stages that extend the viaduct over the M6 and the M6-M42 Link Road requiring two further weekend closures of the motorway.

As each section is added, the weight of the deck will increase from an initial 1,300 tonnes to about 3,000 tonnes by the end of the year, when the finish point will be 4.2 metres higher than the start point. The same technique will be used next year to assemble and slide into place the ‘West Deck’ that will carry two tracks for northbound trains. This second viaduct will require four slides to push it across the road because of the spacing of the piers.

A hollow double-box structure made of weathering steel is being used for both viaduct spans, with the weathering steel providing a natural protective oxidisation layer that gives it a characteristic ‘rusty’ appearance, reducing the need for maintenance by eliminating the need for regular repainting. To support the viaducts, four pairs of concrete piers will be constructed, with the tallest 9.9m high, and there will be a 4.5m high parapet on the Chelmsley Wood side to reduce noise and disturbance from passing trains.

To push the decks forward, a series of winches, known as strand jacks, will be used. These will propel the decks forward at a speed of between six and eight metres per hour, with non-stick pads similar to the material on non-stick frying pans placed on the piers to reduce friction as the decks slide forward.

Elsewhere in the West Midlands, the A46 Kenilworth Bypass was closed in April, and the Cross City line between Birmingham New Street and Lichfield Trent Valley will close for nine days this summer because of HS2 works.

“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.”

Russell Luckhurst, leader of the Balfour Beatty VINCI team constructing the viaducts