The innovative ‘double composite’ design is being used for the 450m long Wendover Dean Viaduct in Buckinghamshire.

It involves two steel girders sandwiched between two layers of reinforced concrete to create a super-strong but lightweight span.

Designed by a team made up of Eiffage, Kier, Ferrovial and BAM Nuttall – working with their design JV partner Arcadis Setec and COWI and architect Moxon – the viaduct is one of 50 being built on the first phase of HS2 between London and the West Midlands.

Applying lessons from the use of double composite structures on the latest French TGV lines, the British team has cut the amount of embedded carbon in the viaduct by 7,433 tonnes – the equivalent of 20,500 return flights from London to Edinburgh.

EKFB’s technical director Janice McKenna said: “This viaduct was inspired by the innovative design in France, but has been enhanced and developed in the context of the Chilterns.”

As well as cutting the amount of concrete and steel, the slender design reduces the silhouette of the structure.

Nine evenly spaced piers, some up to 14m tall, will support the deck of the viaduct and in a further improvement to the original design will now be cast in pieces offsite.

The beams themselves will be made from weathering steel, which will age to a dark russet finish and echo the natural tones of the surrounding landscape. Total steel weight is around 1400 tonnes.

When viewed from a distance, against the weathered steel, the pale concrete parapet will appear as a thin horizontal band hovering over the slender piers making the whole structure look thinner.

HS2’s Project Client Director Ambrose McGuire said: “We’re serious about reducing the amount of carbon we use during construction, and Wendover Dean is a great example of how we’re using the latest engineering techniques to do just that.

“Concrete is one of the construction industries’ biggest sources of embedded carbon – and this design will help us cut our carbon footprint while delivering a lighter, stronger and more elegant structure.”