HS2 viaduct slide over M6 highlights precast concrete role

The M6 has reopened ahead of schedule after HS2 engineers slid part of a new viaduct deck across the motorway — with precast concrete playing a key role in the complex operation.

Over the weekend of 26–28 September, the 230-metre East Deck was moved into position near Birmingham Airport as part of a three-phase programme to install twin viaducts carrying HS2 services between London and the West Midlands.

Although the viaduct decks themselves are formed from weathering steel double-box girders, each is supported by four pairs of reinforced concrete piers, the tallest reaching 9.9 m. To reduce future road closures, the East Deck was launched with 51 precast concrete slabs already installed on top of the structure, forming the base of the viaduct deck.

The slide, carried out by HS2’s main works contractor Balfour Beatty VINCI (BBV) and steelwork specialists Victor Buyck Steel Construction, used strand jacks and non-stick pads to move the 3,400-tonne deck at an average of 10 m per hour.

Caroline Warrington, HS2’s head of delivery, said: “This is a major feat of engineering over a vital section of the UK’s transport infrastructure. These viaducts will be pivotal to the HS2 network, carrying high-speed trains over the M6 and creating better journeys for many years to come.”

The project is part of HS2’s extensive concrete programme, which includes 1.9 million m³ of concrete for structures in the West Midlands alone and more than 83,000 precast tunnel segments for London. Across the line, sustainability measures such as 40% cement replacement with GGBS and the use of steel fibre reinforced concrete (SFRC) in tunnel linings are helping reduce embodied carbon.

Further launches are planned later this year and in 2026. Once complete, the twin 320-metre viaducts will carry high-speed trains over the motorway, with each structure ultimately weighing more than 4,600 tonnes.

For the UK concrete sector, the project demonstrates the integration of precast elements with steel superstructures, as well as the importance of engineered concrete piers and foundations in supporting complex sliding and launch operations over live transport corridors.