HS2’s Thame Valley Viaduct reaches halfway point

Construction of HS2’s Thame Valley Viaduct has now passed the halfway point.

The latest update shows 44 out of 72 customised pre-cast beams are now in position, 66 of the 70 piers have been installed and work is well under way on the deck that will support the railway.

The viaduct near Aylesbury is one of the longest on the high-speed rail project and HS2 says it is a UK-first in terms of the amount of the structure which is being manufactured off-site.

Instead of using a more traditional approach, with multiple narrower beams for each span, the design team opted for a simple structural solution with just two larger hollow 20 or 25m u-shaped beams per span.

These, alongside deck slabs, parapets and all but two of the piers, are being manufactured almost 85 miles away, at a factory on the Isle of Grain, in Kent.

The simple design, inspired by viaducts on the Spanish high speed rail network, allows the beams to be secured end-to-end without concrete being poured on site. 

It also reduces the amount of carbon-intensive concrete and steel in the structure – cutting its carbon footprint by around a third.

Crossing the flood plain of the River Thame, the 880m long viaduct will carry HS2 services between London and Birmingham.

Set low into the landscape with a purposefully simple and consistent profile, the underside of the viaduct will be just 3m above the ground, with 36 even spans crossing the river and surrounding flood plain.

Ben Sebastian-Green, HS2 senior project manager said: “Thame Valley is one of the longest – and from an engineering perspective, one of the most interesting - structures on the project and it’s been great to see so much progress over the last six months.  

“The post-tensioned double-beam approach used here has enabled more of the viaduct to be manufactured off-site - dramatically improving efficiency, safety and quality while delivering outstanding performance and durability.”

The viaduct was designed by HS2 main works contractor, EKFB - a team made up of Eiffage, Kier, Ferrovial Construction and BAM Nuttall - working with specialist on-site construction partner, FC Civils Solutions.

Following the success of the design, a similar approach is now also being used for the nearby Edgcote Viaduct in Northamptonshire.