HS2 engineers have dramatically cut the carbon footprint of five major viaducts by as much as 66 per cent through using an innovative ‘double composite’ structure that requires much less concrete and steel.

Revealed by HS2 today, the design was rolled out to viaducts in Buckinghamshire, Oxfordshire, and West Northants after efficient results at HS2’s first double composite viaduct at Wendover Dean, inspired by lessons from European rail projects.

Traditionally, single composite structures have been used in the UK, where steel beams support a reinforced concrete deck between the viaduct piers.

By adding a concrete bottom to create a hollow box-like structure, the double composite approach is far more efficient, reducing the overall thickness of the concrete and steel used.

As production of these two materials contributes hugely to carbon emissions for the construction industry, this novel move allowed the team to cut embedded carbon in the five viaducts by between 52 and 66 percent.

These viaducts, located at Westbury, Turweston, Wendover, Small Dean and Lower Thorpe, were designed by HS2’s chief works contractor EKFB (a team comprising Eiffage, Kier, Ferrovial Construction and BAM Nuttall) in collaboration with ASC and architects Moxon.

HS2 Ltd’s Head of Civil Structures, Tomas Garcia, said: "HS2 will improve journeys between Britain’s two biggest cities while freeing up more space on the most overcrowded parts of the existing mainline for more local services.

"Construction is well underway, and it’s great to see the lessons learnt from Wendover Dean, rolled out to four other major structures".

One of the viaducts is near Brackley, where work has started to slide the 320-metre-long double composite deck into position.

This deck changes, coupled with the usage of lower-carbon concrete and steel and alterations to foundations, the design team cut the amount of embedded carbon in Westbury viaduct by 60%.

Jose Candel, EKFB’s Design Delivery Director, said: "The double composite design of this group of viaducts spanning Bucks and Northants, is exemplary in the UK.

"It enables a high degree of off-site manufacturing.

"This industry-leading approach is innovating and paving the way for future infrastructure projects".

All of the viaducts will be assembled in stages and slid into position.

The process requiring approximately 11 hours to push each deck out from the north abutment before the subsequent section is attached behind it.

Gerard Brennan, ASC Viaducts Lead Engineer and Technical Director, COWI in the UK, said: "The ASC team is proud to have contributed to the design of these innovative structures, which have been optimised for minimum material use and maximum embedded carbon reduction".

Significant progress has also been noted in other major viaducts, the largest among them being the Delta Junction and a half-kilometre deck slide at Wendover Dean.

In total, HS2 is building more than 500 bridging structures.