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Wed July 28 2021

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Innovative design for Chilterns viaduct

20 Jul A viaduct in the Chilterns is set to be the UK’s first to have a double composite design.

Wendover Dean Viaduct – they've tried not to make it an eyesore
Wendover Dean Viaduct – they've tried not to make it an eyesore

Wendover Dean Viaduct in Buckinghamshire will be made from two steel girders sandwiched between two layers of reinforced concrete for maximum strength and minimum weight.

It is one of 50 viaducts on the first phase of the HS2 high speed railway line between London and the West Midlands. It is being built by EKFB, a joint venture of Eiffage, Kier, Ferrovial and BAM Nuttall, HS2 Ltd’s main works contractorfor the 80km section between the Chiltern Tunnel and Long Itchington Wood.

At 450-metres long, Wendover Dean Viaduct is one of the most substantial structures that EKFB will be building. It has been designed by ASC, a joint venture between Arcadis Setec and Cowi, with specialist architect Moxon, who have based their design on the double composite approach used in French TGV rail construction.

Making the structure super sleek takes out excess material,which removes cost and embedded carbon – 7,433 tonnes of the stuff. The designers have also sought to avoid creating an eyesore across the countryside by minimising its obtrusiveness.

The deck is carried across the valley on nine evenly spaced piers, up to 14 metres high. These will be precast in sections offsite.

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EKFB 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. Our design solutions are always created with people and legacy in mind and I am really proud of the carbon savings that the Wendover Dean Viaduct represents.”

The beams themselves will be made from weathering steel, which should age to a characteristically dark russet finish. Total steel weight is around 1,400 tonnes and will be topped with a concrete deck that will carry the track.

According to HS2’s publicity material: “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 as it glides over the valley and make the whole structure look thinner. This effect will be further emphasised by the viaduct piers, which have been extended to almost connect with the parapet, helping to give the appearance of a light and narrow structure.”

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