HS2 ramps up work on concrete deck of the UK’s longest railway bridge

Credit: HS2

Work on the UK’s longest railway bridge ramped up as HS2 began production of 1,000 enormous concrete segments that will form the deck of the Colne Valley Viaduct. Stretching for 2.1 miles across a series of lakes and waterways just outside London, the viaduct will carry high-speed trains as part of the HS2 project, designed to improve rail links between London, Birmingham and North, boost the economy and provide a low carbon alternative to car and air travel.

The huge deck segments, which weigh up to 140 tonnes, are being made on site at a temporary factory built specifically for the project. The mammoth 100m long building, which is visible from the M25, has an internal volume of 105,000 cubic metres, making it larger than the Royal Albert Hall.

“We’re already making strong progress on the Colne Valley Viaduct, sinking the foundations, building the first piers, and now starting production at the new modular viaduct factory,” David Emms, HS2 Project Client, said. “Once complete, this iconic structure will carry trains at up to 200mph, improving connections across the UK, freeing up rail capacity and offering passengers low carbon travel options. It is great to see how much progress has been made and I look forward to seeing work on assembling the deck structure later this year.”

Every segment will be a slightly different shape depending on where it fits into the viaduct and the modular approach was chosen to ensure quality, safety and efficiency in production and to avoid bringing them in by road.

At the peak of construction, around 12 segments, each the size of a double-decker bus, will be cast every week using a match-casting technique. This approach, where each segment is poured against the previous one, will ensure the whole arch fits perfectly when reassembled on site. The huge project is being led by engineers from HS2’s main works contractor Align JV, a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.

Once construction is complete, the factory and surrounding buildings will be removed and the whole area between the viaduct and the Chiltern tunnel will be transformed into an area of chalk grassland and woodland as part of HS2’s green corridor project.

“Seeing the first deck segments being cast in the factory marks a significant milestone for the project,” Daniel Altier, Project Director at Align, said. “The design of the viaduct is such that each segment will be unique, delivering a structure which I have no doubt will be one of the most striking elements of HS2 once complete.” 

The design of the Colne Valley Viaduct was inspired by the flight of a stone skipping across the water, with a series of elegant spans, some up to 80m long, carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal. Set low into the landscape, wider spans will carry the viaduct crosses the lakes, with narrower spans for the approaches. This design was chosen to enable views across the landscape, minimise the viaduct’s footprint on the lakes and help complement views across the natural surroundings.