Construction of one of the longest viaducts on the HS2 rail project recently passed the halfway mark thanks to innovative methods.
The 880-metre-long Thames Valley Viaduct, near Aylesbury, in Buckinghamshire, has 44 of its 72 custom pre-cast beams in position as well as almost all of its 70 concrete piers weighing 42 tonnes each.
It was designed by main contractor EKFB (Eiffage, Kier, Ferrovial Construction and BAM Nuttall), working with specialist on-site construction partner FC Civils Solutions.
The team opted for a simple structural solution during design, utilising just two larger, hollow 20 or 25-metre U-shaped beams weighing 90 tonnes each, instead of multiple narrower beams per span, of which there are 36 in total.
These, alongside deck slabs, parapets and all but two of the piers, are being manufactured off site at a PACADAR UK factory in Kent.
The design allows the beams to be secured directly to one another end-to-end using a 10-man team over around three hours, without the need to create a concrete connecting ‘diaphragm’ which is traditionally cast in situ.
It also reduces the amount of carbon-intensive concrete and steel in the structure, cutting its carbon footprint by around a third.
Once the beams are in place, steel bars are threaded between the beams which are then post-tensioned to give the viaduct the structural strength to support trains travelling at speeds of up to 225 mph.
Following the success of the EKFB design, a similar approach is now being used for the nearby Edgcote Viaduct in Northamptonshire.
Ben Sebastian-Green, HS2 Limited’s 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.”
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