HS2 | Construction passes halfway on prefabricated 880m Thame Valley Viaduct

The contractor has now placed 44 of 72 customised 25m long, 90t precast beams into position, installed 66 of 70 precast piers and is “well underway” on creating the deck that will support the railway, according to HS2 Ltd.

The Thame Valley Viaduct is low-lying, with the underside 3m above the flood plain beside Aylesbury in Buckinghamshire.

The precast design was developed by EKFB in collaboration with ASC (a joint venture between consultants Arcadis, Setec and Cowi), architect Moxon and Ferrovial subsidiary FC Civils Solutions.

Earlier this year, NCE learned how the initial design of the viaduct was to be much more conventional, but the team took inspiration from Spanish high-speed rail viaducts for a much more time and carbon efficient construction.

Instead of using multiple narrower beams for each span, the Thame Valley viaduct has two larger, hollow, prefabricated u-shaped concrete beams per span. This allows the beams to be secured end-to-end, unlike traditional bridges which see the concrete poured on site to create a diaphragm. To secure the Thame Valley Viaduct beams, engineers thread steel bars between holes in the ends of the beams and post-tension them to lock them together.

This approach also means that work progresses quicker, with engineers installing six beams per week in the first six months of assembly. On average, a team of 10 people can install a beam in around three hours.

Further advantages include a reduction in the amount of concrete and steel, which reduces carbon by a third, and less need for working at height.

As well as the beams, the parapets, deck slabs and all but two of the piers are being manufactured by Pacadar on the Isle of Grain in Kent, 138km away.

The two non-precast piers are at the centre of the viaduct and have been cast insitu. Whereas the rest of the piers will allow slight movement of the deck on top to accommodate for thermal expansion and acceleration forces, these two fixed piers are bigger than those piers to provide stability and handle the horizontal forces that are transferred to the deck.

The prefabricated approach to the Thame Valley Viaduct has been so successful that EKFB has adopted it for the 550m Edgcote viaduct in Northampton.

HS2 Ltd 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.”

EKFB 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.”

 

Source: https://www.newcivilengineer.com/latest/hs2-construction-passes-halfway-on-prefabricated-880m-thame-valley-viaduct-20-05-2024/

Source: NewCivilEngineer.com