Final concrete works complete on HS2’s Colne Valley Viaduct

Construction of the UK’s longest railway viaduct – the 3.4 km Colne Valley Viaduct – is now complete, marking a key milestone in the HS2 programme and a significant achievement for Align JV’s concrete and civil engineering teams.

Spanning land and water between the Chiltern Tunnels and the London approach to Euston, the viaduct will carry high-speed trains travelling at up to 320 km/h (200 mph). The structure has been recognised for its distinctive, sweeping curve across the Colne Valley landscape.

The viaduct deck was constructed using 1,000 precast concrete segments, each weighing up to 140 tonnes and produced on site to bespoke geometries. These were lifted into place by ‘Dominique’ – a 160-metre launching girder – with the final segment installed in September 2024.

Following deck installation, Align’s finishing teams carried out a range of critical concrete works. Over 3,600 m³ of in-situ concrete was poured to form the kerb system. The high-performance waterproofing membrane protecting the structure is overlaid with a 100 mm thick steel fibre reinforced concrete slab, providing enhanced durability and crack resistance.

Concrete-related tasks also included installation of the internal drainage systems, placement of structural monitoring elements, and construction of 4 m high noise barriers flanking both sides of the viaduct.

“This viaduct presented a significant engineering challenge, both in terms of precision and scale,” said a spokesperson for Align JV. “By working as a fully integrated team and collaborating closely with our supply chain, we’ve delivered what we believe will be one of HS2’s most iconic structures.”

Precast and in-situ concrete works were supported by a wide network of suppliers and contractors, including Kilnbridge, J Coffey Group, and Tarmac, with testing and assurance by SOCOTEC.

The viaduct now stands as a testament to the critical role of concrete engineering in HS2’s infrastructure – both for its structural integrity and long-term performance. It also highlights the benefits of segmental precast construction on major rail projects, offering consistency, quality control and reduced environmental impact.

HS2 and Align JV expect finishing works to continue into 2026, ahead of the viaduct’s commissioning.