HS2 begins assembling UK’s first offsite viaduct as cost of delays revealed

Assembly of the UK’s first major railway viaduct to be manufactured entirely off-site has begun in Buckinghamshire. 

The 880m-long Thames Valley Viaduct will eventually carry HS2 services over the flood plain of the River Thame, just outside Aylesbury. 

HS2 is the Europe’s biggest ongoing infrastructure project but news of the latest progress on the job came on the day of a leaked government briefing, which revealed delays to the phasing of HS2, announced earlier this year to save costs, were likely to cost the taxpayer £366m. 

The report also predicted that the two-year pause applied to work on Euston station and phase 2b would actually last around three-and-a-half years because of the additional time needed to ramp up work. 

According to HS2, the off-site approach to building the viaduct improves efficiency as well as cutting its carbon footprint by around a third. 

Unlike traditional viaducts, the 68 giant concrete piers which comprise the Thame Valley Viaduct are being manufactured at PACADAR’s factory on the Isle of Grain in Kent before being transported to site by road and slotted together. 

It was designed by EKFB – a joint venture of Eiffage, Kier, Ferrovial Construction and BAM Nuttall – working with specialist on-site construction partner, FC Civils Solutions. 

EKFB was recently replaced on parts of phase one of the job by another joint venture, Align, as part of HS2’s efforts to streamline the central section of the railway. 

>> In pictures: how Align JV is building the UK’s longest rail bridge, one piece at a time

>> New Arcadis boss latest to query ‘baffling’ HS2 Euston decision

The design team opted for a simple structural solution with two 25m long hollow beams per span, which allowed them to cut the amount of carbon-intensive concrete and steel used while simplifying work on site. 

“Thame Valley may not be HS2’s biggest viaduct, but it does represent a major step forward in terms of its structural design,” said Tomas Garcia, HS2’s head of civil structures.  

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

“Once complete, HS2 will offer zero-carbon journey across the UK, but structures like this will also help us develop new ways to cut embedded carbon in construction that can be adopted across the rest of the industry in the future. That’s why it’s great to see the first piers in place as our construction partners begin to assemble this ground-breaking viaduct.”