First beams for HS2’s 'double composite' low carbon Wendover Dean Viaduct arrive on site

High Speed 2 (HS2) is due to begin the deck construction of a 450m long viaduct in Buckinghamshire as the first of 38 steel beams for the low carbon structure have arrived on site.

Weighing 40t and 25m in length, the beams have travelled more than 900km to reach the site after being manufactured by Eiffage Metal in a specialist facility in France.

The Wendover Dean Viaduct will be the first major railway bridge in the UK to be built with a “double composite” structure, using significantly less carbon-intensive concrete and steel than a more traditional design.

Instead of using solid pre-stressed concrete beams to form the bridge spans, the viaduct will use two steel beams sandwiched between two layers of reinforced concrete to create a lightweight and super strong hollow span. All the spans will be assembled on-site with the pre-cast concrete sections added after to form the box-like structure before being pushed out onto the nine piers from the north abutment. The total steel weight of the viaduct once completed will be around 1400t and will be topped with a concrete deck which will carry the track and built-in noise barriers.

The viaduct is being constructed as part of phase one of the UK’s high speed rail project by main works contractor EKFB, a joint venture between Eiffage, Kier, Ferrovial Construction and Bam Nuttall.

Located just south of the village of Wendover in Buckinghamshire, the viaduct was designed by EKFB in conjunction with its design partner ASC, a joint venture between Arcadis, Setec and Cowi and architects Moxon. The double composite design was inspired by structures on the French high speed TGV rail network.

Each of the beams is made of weathering steel which HS2 has stated will naturally fade to a dark brown colour over time and was chosen to help “match the natural tone of the surrounding countryside".

HS2 project client Neil Winterburn said: “It’s great to see the first beams arrive on site. These huge pieces of steel will play a vital role in the innovative double composite structure of the viaduct deck – and help us cut the amount of embedded carbon in the structure.

“As well as offering zero carbon rail travel, it’s also important that we reduce the amount of carbon intensive steel and concrete we use in construction. That’s why this viaduct and this structural design is so important.”

HS2 believes the double composite approach will save an estimated 7,433t of embodied carbon within materials used for the construction.

Over the summer, the beams will be assembled by Eiffage to form the first of five 90m long spans to be pushed onto the under-construction viaduct piers later in the year.

EKFB’s senior engineer James Collings said: “There's been a tremendous amount of effort put in to get to this stage of construction, including an extensive earthworks and utilities programme and beam delivery is a key milestone for the team.

“As momentum gathers pace and we continue our preparations for the bridge deck launch, it’s great to see these steels on site, ready for the next phase of build. We’re starting to see the viaduct emerge from its foundations and start to take shape above ground.”

While the beams were under manufacture, construction on the nine piers, some reaching 14m in height, has been progressing. The piers are made of a series of hollow pre-cast concrete shells which will be assembled on-site and filled with concrete and steel reinforcing.

Foundation work began on the viaduct in July last year with the formation of the first of the 53 concrete piles.

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