The 320m-long viaducts are being built to one side of the motorway before being slid into position during a series of weekend closures to minimise disruption.

The first double box steel structure is set for its first 119m launch over a slip road during the weekend of 7/8 June.

Strand jacks will be used to push the decks forward at a speed of 6-8m per hour,

Two further weekend closures will follow as the structure slides across the motorway and the M6-M42 link.

Specialist steelwork contractor Victor Buyck is supporting the launch alongside National Highways.

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.

The deck will be pushed uphill by 4.2 metres using strand jacks and low-friction PTFE pads.

How finished 320m-long viaduct will look once finished

Russell Luckhurst, project director for Balfour Beatty Vinci, said: “We’re entering an exciting phase as the first steel section begins to take shape. Launching the decks offline in phases will help us reduce the impact on road users.”

HS2 senior project manager Liam Kenney added: “This is a hugely complex job and the multi-stage approach will help minimise disruption.”

The second viaduct, the ‘West Deck’, will be slid out in 2026 using the same method.

Both structures use weathering steel with a double-box design and are supported by four pairs of concrete piers, the tallest standing 9.9m high. A 4.5m high parapet will be installed to reduce train noise near Chelmsley Wood.

The operation draws on lessons learned during the delivery of the nearby M42/M6 link viaducts.