HS2 slides final double composite viaduct
Engineers working on HS2 have completed the three-day installation of the Lower Thorpe viaduct deck near Thorpe Mandeville in West Northamptonshire, sliding the 1,300-tonne concrete and steel structure into place across five piers.
Delivered by HS2’s central section contractor EKFB – a joint venture of Eiffage, Kier, Ferrovial Construction and BAM Nuttall – the 220 m-long viaduct is the last of five ‘double composite’ structures to be installed using this sliding method. It will eventually carry high speed trains over Banbury Lane and help manage flood risk through the local valley.
The viaduct deck, made from russet-toned weathering steel and concrete, was constructed to the side of its final location and slid into place between 18 and 20 June. Polytetrafluoroethylene (PTFE) pads, similar to non-stick coatings, were used to reduce friction between the deck and the temporary steel bearings during the move. It will now be lowered 60 cm onto permanent bearings, after which work on the concrete deck and parapets will begin.
“This slide may only have taken three days, but it was the culmination of four years of work,” said HS2 Ltd project manager Sam Arrowsmith. “From design development and groundworks to assembling the enormous steelwork, this has been a major collaborative effort.”
The Lower Thorpe viaduct is built using a double composite structure that replaces traditional solid pre-stressed beams with hollow spans combining steel side girders and concrete slabs above and below. This design allows for longer spans and shallower beams, while reducing material use and embedded carbon by up to 59% compared to conventional approaches.
EKFB technical director Janice McKenna said: “The strategic design approach applied to these double composite structures has been a game-changer. They’ve been designed not only to reduce carbon and cost but to blend into the landscape and improve on-site safety.”
EKFB is delivering 15 viaducts in total along its 80 km stretch between the Chilterns and South Warwickshire. The other four double composite viaducts – Wendover Dean, Small Dean, Turweston and Westbury – are all at more advanced stages. At Westbury, the deck is now being cast using a cantilever formwork traveller, which improves efficiency and reduces the need for cranes.
Once complete, the viaduct will carry HS2 trains between London and the West Midlands, freeing up capacity on existing railways for freight and regional services.
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