The 345-metre long viaduct is the latest structure to gain design approval on the UK’s biggest infrastructure project.
Set low into the landscape, the viaduct’s girders will be made from weathering steel, designed to age naturally to a dark russet finish to fit the natural tones of the surrounding landscape.
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 six metres above the road, supported by five Y-shaped piers.
The side of the girders will have prominent deck stiffeners to help bear the structural forces while allowing for a lighter beam. The piers are also 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 super strong but lightweight span – substantially reducing the embedded carbon in the structure. [See our previous report here.]
Both viaducts were designed by HS2 Ltd’s main works contractor, EKFB – a joint venture of Eiffage, Kier, Ferrovial Construction and Bam Nuttall – working with engineering consultant ASC (a joint venture of Arcadis, Setec and Cowi) and architect Moxon.
HS2 Ltd design director Kay Hughes said: “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.”
Once complete, the viaduct will carry high speed trains between London and Birmingham. After crossing the viaduct, northbound trains will pass the town of Wendover in a short tunnel. Most of the elements of the tunnel’s south portal and associated noise barriers were also given ‘planning approval’ this week under Schedule 17 of the HS2 Act.
EKFB 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: “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, before the 5,800 tonne deck will be launched in 2025.”
Moxon managing director Ben Addy said: “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.”
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 terraces to manage the change in height between road, paths, railway and viaduct.
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