GREEN LIGHT FOR HS2’S SMALL DEAN VIADUCT

The striking 345m long viaduct is the latest major structure to gain design approval, as construction continues to ramp up on the UK’s new high-speed railway.

Set low into the landscape, the viaduct’s enormous girders will be made from weathering steel, which naturally ages to a characteristically dark russet finish to echo the natural tones of the surrounding landscape. Designed to be seen from close-up, the viaduct is one of only two places in the Chilterns where the HS2 route will be above ground level, with the underside of the viaduct just 6m above the road, supported by five ‘Y’ shaped piers.

Echoing the great railway bridges of the Victorian age, the side of the girders will feature prominent deck stiffeners which help to manage the structural forces while allowing for a lighter weight beam.

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, appearing to reach up and grip the beam above.

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



Once complete, the viaduct will carry high-speed trains between London and the North, helping to improve connections, free up space for more freight and local trains on the existing railway and provide zero-carbon journeys for people across the UK.

As well as the main road, the viaduct will also span the neighbouring Chiltern line to London Marylebone and the project will also include the realignment of Small Dean Lane. The A413 will be realigned to pass under the viaduct, with landscaping in the form of a series of subtle terraces to manage the change in height and interplay between road, paths, railway and viaduct.

A shared foot and cycle path will also be delivered by HS2 alongside the main road as it passes under the viaduct between the A413 London Road roundabout and the houses near Rocky Lane. This will eventually form part of the Misbourne Greenway project designed to link Wendover with Great Missenden.