First section of M6 South viaduct slides into position thanks to non-stick material

Using material similar to that found on non-stick frying pans, the first of three giant sections was moved into place during a 29-hour closure. The ‘East Deck’ section was slid 119 metres out over a slip road adjacent to the motorway, and the road reopened 11 hours ahead of schedule.

The viaduct deck is being assembled to one side and slid across the motorway over three weekends, with each part pushed out before later sections are added behind them. This multi-stage process means that the weight of the deck will increase with each push from 1,300 tonnes for the first slide, to 3,290 for the final one, which will take the deck out over the main M6 carriageway and then finally the M6-M42 link roads.

The East Deck will carry two tracks taking trains towards London while an adjacent West Deck will carry a further two tracks for services heading to Birmingham and further north. This will be assembled and slid out next year using the same technique.

Each viaduct span is 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 support the viaducts with tallest one 9.9m in height. A 4.5m high parapet will be provided on the side facing the Chelmsely Wood to reduce noise and disturbance from passing trains.

The structural design has been carried out by Balfour Beatty VINCI’s Design Joint Venture (DJV), made up of Mott MacDonald and SYSTRA.

Tom Dutton, Senior Design Co-ordinator for the Mott MacDonald SYSTRA DJV, said: “The launch of the first deck of the two-deck M6 Motorway South Viaduct marks an exciting milestone following years of dedicated design work. We have seen the design take shape as the foundations, piers, and abutments were constructed, and now the moment has arrived for the deck to be launched.

“The launch design is a fantastic example of collaboration between Mott MacDonald SYSTRA DJV colleagues in the UK and France, BBV, and their steelwork and launching contractor, Victor Buyck Steel Construction. Together, we have addressed the complex challenges of the temporary works and the fabrication of the steel diaphragm—not to mention the feat of launching the viaduct decks over the M6 motorway itself.

“This achievement is a testament to our collective effort and a fantastic milestone for the immediate team and the whole project.”