Small Dean Viaduct

The striking 345m long Small Dean Viaduct, just south of Wendover, has gained design approval and will carry the HS2 line across the A413, Small Dean Lane and the Chilterns rail line.

After crossing the viaduct, northbound trains will pass the town of Wendover in a short tunnel designed to reduce the environmental impact of the scheme.

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.

Viaduct construction

Critical preparatory work has been completed with engineers working safely on two of the huge viaduct piers that will support the viaduct to build the 49m deep piled foundations for the pier just 5m east of the railway and lifting a 42 tonne ‘Y’ shaped pre-cast segment onto the pier west of the railway.

As well as the construction of the viaduct, HS2 will also realign Small Dean Lane and the A413 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.

Viaduct design

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 that 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.