HS2 unveils Thame Valley Viaduct design

Thame Valley Viaduct HS2 has revealed the final designs for the Thame Valley Viaduct and the pioneering pre-fabricated construction methods that will see the 880m long structure slotted together like a giant Lego set, cutting its carbon footprint by an estimated 66%.

Set low into the landscape with a simple and consistent profile, the underside of the viaduct will be just 3m above the ground, with thirty-six 25m long neat and even spans crossing the river and surrounding wetlands. The piers will be extended to almost connect with the parapet edge, helping to enhance the appearance of a light and narrow structure.

Thame Valley is one of 15 viaducts designed by HS2 Ltd’s main works contractor, EKFB, a team made up of Eiffage, Kier, Ferrovial Construction and BAM Nuttall which is working with their design partner, ASC (a joint venture between Arcadis Setec and COWI) and specialist architects Moxon.

The design team cut the amount of embedded carbon by simplifying the structure of the viaduct so that every major element can be made off site. In a major step forward for viaduct design in the UK, the team opted for two wide ‘box girder’ beams per span instead of eight smaller beams – to simplify and speed up assembly.

The production of steel and concrete is a major contributor to carbon emissions, with the new lighter-weight structure expected to save 19,000 tonnes of embedded carbon in comparison to the previous design. That’s the same amount of carbon emitted by one person taking a flight from London to Edinburgh and back 70,000 times.

As well as cutting embedded carbon in terms of materials, this approach requires less lorries to deliver material to site, cuts waste and will reduce disruption for the community during construction.

“(…) Thame Valley is a great example of how our contractors are using the latest engineering techniques. Prefabrication and off site manufacturing offer huge benefits in terms of efficiency and this design will help us deliver a more efficient, durable and elegant structure with less concrete and steel,” Tomas Garcia, HS2 Ltd’s Head of Civil Structures said.

The 35 concrete piers that support the viaduct will also be entirely made off site before being placed on their foundations which means that every major element of the structure will be pre-fabricated. Traditionally, viaduct beams are secured together above each of the piers with a concrete diaphragm which is cast in situ. The larger pre-cast beams that will be used at Thame Valley can secured directly to one another, removing the need for the diaphragm, improving durability and reliability, saving time, cutting cost and improving safety by reducing the need for people to work at height.

The Thame Valley Viaduct will cross the flood plain of the River Thame, just outside Aylesbury, and will carry HS2 trains at speeds of up to 360 km/h between London, Birmingham and the North.

Preparatory works have already begun on site near Aylesbury, with the design team also looking at whether a similar modular approach to construction can be applied to other, smaller viaducts elsewhere on the route.


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