Buckinghamshire Council has given the green light to Small Dean Viaduct, which will take HS2 trains across the A413 and local rail lines south of Wendover.

The viaduct’s girders will be made from weathering steel, so that it will age to a dark russet finish to echo the tones of the surrounding landscape. The structure has also been designed to echo the great railway bridges of the Victorian age, with the side of the girders featuring prominent deck stiffeners to help manage the structural forces while allowing for a lighter weight beam.

The 345m-long Small Dean Viaduct will feature weathering steel

The underside of the viaduct will be just 6m above the road, supported by five Y-shaped piers.

The pale concrete parapet and noise barrier along the top of the viaduct is designed to throw the dark steel into shadow, helping to give the appearance of a lighter and thinner structure. The piers are designed to be as slender as possible.

Structurally, the viaduct girders will use a ‘double composite’ approach, like the nearby Wendover Dean Viaduct. This involves two steel girders sandwiched between two layers of reinforced concrete to create a strong but lightweight span, designed to cut the amount of embedded carbon in the structure.

Both viaducts were designed by HS2 Ltd’s main works contractor, EKFB - a team made up of Eiffage, Kier, Ferrovial Construction and BAM Nuttall - working with design partner, ASC (a joint venture between Arcadis Setec and Cowi) and specialist architect Moxon.

HS2 Ltd’s design director Kay Hughes said: “By providing a cleaner, greener way to travel, HS2 will help cut the number of cars and lorries on our roads, cut demand for domestic flights, and help the fight against climate change.

“But it’s also vital that we cut carbon during construction, and the innovative approach to Wendover’s Small Dean Viaduct is a great example of how HS2 can deliver elegant viaducts at a fraction of the normal carbon footprint and save construction time. I’d like to congratulate the design team and look forward to seeing this outstanding viaduct start to take shape over the coming years.”

EKFB’s interface and stakeholder director, Simon Matthews, said: “Small Dean Viaduct is the most high-profile of the 15 viaducts that we are delivering across our 80km central section of high speed 2, and we have been developing our design to respond to the unique challenges of building a sustainable structure that responds to the local environment.”

He added that works are already under way to prepare for the new viaduct, and over the next two years the foundations and piers will be built alongside the busy A413 road, before launching the 5,800t deck in 2025.

Moxon managing director Ben Addy said: “We’re delighted with the news that Small Dean Viaduct has achieved planning consent, a decision that comes after a productive, design-driven dialogue between the team and Buckinghamshire Council officers on the final proposals.

“The character of the site, combined with the pronounced diagonal alignment and low deck level, will result in an especially dynamic appearance when viewed from the carriageway, and evoke a sense of infrastructural grace as the deck passes overhead through the tree canopy.”