HS2 unveils final designs for Moxon’s Thame Valley viaduct

HS2 has unveiled the final designs of an 880m-long bridge designed by Moxon Architects that will be almost entirely built with prefabricated components.

All major sections of the Thame Valley viaduct will be manufactured off site and “slotted together like a giant Lego set”, the £100bn railway project has said.

HS2 said the approach, which has been inspired by recent high speed rail projects in Spain, would cut carbon during construction by as much as two thirds.

The bridge will carry trains travelling at speeds of up to 360km per hour over the flood plain of the River Thame, just outside Aylesbury in Buckinghamshire.

Described by Moxon as a “minimalist elevated causeway”, it will be set low into the landscape with the underside of the structure just 3m above the ground.

Consisting of 36 even spans, each 25m-long, it will be built by assembling its modular pre-cast beams directly against each other.

This differs from traditional bridge construction, which involves securing the beams using a concrete diaphragm which is cast in situ.

The lighter-weight structure is expected to save around 19,000 tonnes of embodied carbon compared to previous designs for the bridge, according to HS2.

The scheme’s main contractor EKFB - a joint venture between Eiffage, Kier, Ferrovial and Bam Nuttall - said the process of cutting carbon started at the initial design stages.

The Thame Valley viaduct is one of 15 bridges designed by EKFB as part of HS2’s route, which stretches from London Euston to Manchester.

The longest, the 3.4km Colne Valley viaduct, will also be the UK’s longest rail bridge when completed and will carry passengers between a pair of tunnels beneath central London to the 16km long Chiltern tunnels near the M25.

Unlike the bridge over Thame Valley, the Grimshaw-designed Colne Valley viaduct will consist of a series of spans of different lengths with some nearly 80m long.

Meanwhile, EKFB has put firms on notice for a £7m contract to build a protective mesh to prevent bats being hit by HS2 trains. The JV is seeking a subcontractor to build the 900m long ‘Bat Mitigation Structure’ in Buckinghamshire.

The section runs alongside Sheephouse Wood, an ancient woodland which is designated as a site of special scientific interest and which is also home to several bat species, including the rare Bechstein’s bat.

The contract includes the installation of pre-cast concrete arches and fibreglass mesh panels. Closing date for interested parties is 21 April, with the work set to begin in February 2024 and end the following May.