Engineers working on the HS2 project have completed construction of the 320-metre Westbury viaduct, which will carry high-speed trains across the floodplain of the River Great Ouse near Brackley.
Set low in the landscape to the east of the town, Westbury is the longest viaduct in the Brackley area and is one of 15 viaducts being constructed by EKFB, the main works contractor responsible for the central section of the HS2 route. EKFB is a joint venture between Eiffage, Kier, Ferrovial Construction and BAM Nuttall.
Innovative double composite design
The viaduct uses an unusual ‘double composite’ construction approach, inspired by recent viaducts on France’s TGV network.
Rather than using a conventional concrete span or a steel beam supporting a concrete deck, the design incorporates reinforced concrete both above and below the steel beam. This creates a more efficient box-beam structure and reduces the quantities of carbon-intensive concrete and steel required.
The steel beams alone weigh 2,695 tonnes. They were assembled on the northern abutment before being slid into position between March and October 2024.
Special pads with a non-stick coating were used during the slide to minimise friction between the deck and the temporary steel bearings positioned on top of the concrete piers.
Construction completed
Once the steel beams were in place, a travelling formwork system was used to cast the concrete deck in 42-metre sections. The formwork was progressively moved forward after each section was completed, allowing the next section to be cast.
With the deck complete, prefabricated parapets were lifted into position along the edges of the viaduct and secured in place.
The completion of the structure marks another significant milestone in the construction of the central section of HS2. Nearby works have also progressed, including the Turweston green bridge, completed in April, and the realignment of the A43, completed in July.
The hardstanding surface installed beneath the viaduct to support heavy construction equipment will now be removed, with landscaping works to follow.
Westbury Viaduct demonstrates the scale of engineering involved in delivering a new high-speed railway, as well as the opportunities to apply design approaches developed on high-speed rail networks elsewhere in Europe to improve construction efficiency and reduce material requirements.
HS2 Ltd’s Senior Project Manager, Paul Cooper said:
“It’s been amazing to watch Westbury viaduct come together over the last few years and I’d like to thank everyone involved in getting this incredible structure over the finishing line.
“This section of the railway is now really starting to come together, and with the viaduct complete, our focus will turn to completing the earthworks and other nearby structures.”