HS2's Thame Valley Viaduct, one of the longest on the high-speed rail project, recently passed the halfway point of its construction, with significant progress on its innovative design.

The viaduct, located near Aylesbury, stands as a first for the UK due to the amount of the structure being produced off-site.

With 44 out of 72 custom-made pre-cast beams now in place and work well under way on the supporting deck, the project's completion is fast approaching.

Instead of adopting a conventional strategy involving multiple narrower beams per span, the design team chose a straightforward structural solution comprising two larger 20 or 25m u-shaped beams.

The design was inspired by viaducts on the Spanish high-speed rail network and has several benefits.

These beams, in conjunction with deck slabs and all but two of the piers, are being manufactured nearly 85 miles away on the Isle of Grain, in Kent.

This streamlined design allows the beams to be affixed end-to-end without the need for onsite concrete pouring and cuts the structure's carbon-intensive concrete and steel content, reducing its carbon footprint by approximately a third.

HS2 Ltd’s Senior Project Manager, Ben Sebastian-Green, 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."

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

The overhaul will improve journeys and create more space for additional freight and local services on the current network.

Both the viaduct's low placement into the landscape and its streamlined, consistent profile mean it will stand just 3m above ground level.

The innovative construction approach also reduces the number of lorries needed to transport materials to the site, simplifies the build process, minimises waste, and decreases local disruption.

Additionally, site safety is enhanced by diminishing the amount of work conducted at height.

Following the design’s success, a similar tactic is now being used on the nearby Edgcote Viaduct in Northamptonshire.

Typically, viaduct beams, even those built off-site, are fastened above each of the piers with a concrete diaphragm, cast in situ.

However, the larger pre-cast beams used at Thame Valley and Edgcote can be attached directly, removing the need for the diaphragm.

The progress on Thame Valley Viaduct exemplifies the advantages of off-site manufacturing, which not only speeds up on-site work but also creates job opportunities across the UK.

About 200 individuals, including apprentices and graduate engineers from local universities, are currently working at the Isle of Grain facility alone.

The construction is an essential part of HS2's initiative to dramatically improve journeys and free up space for more freight and services in the existing network.

EKFB’s Project Manager, Emma Bolado-Arroyo, said: "We’re at a crucial and exciting stage with the construction of this innovative viaduct, with beams, piers, post tensioning and pre-cast slabs under construction.

"This incredible progress is a testament to the hard work and drive of our expert teams.

"We’re all very excited to see this structure being delivered safely and to programme."