Major milestone for HS2 viaduct


The London section of the programme welcomes the completion of the first set of piers for the UK’s longest railway bridge.

Photo of the Colne Valley Viaduct site.
Credit: VolkerFitzpatrick.

The Colne Valley Viaduct is located near Hillingdon and the M25 and will carry high-speed trains more than 3.4km across the Grand Union Canal, River Colne, local roads and a series of lakes between the end of the London tunnels and the start of the Chiltern tunnels.

Align JV are the main works contractor for the bridge, comprising Bouygues Travaux Publics, Sir Robert McAlpine, and Volker Fitzpatrick.

The team began construction in 2021 and expects to complete the viaduct by May 2025

Inside the job

160m launch girder, weighing 700 tonnes, is assembling precast concrete piers to form the first 1km of the viaduct deck. 

The girder has installed more than 300 out of the 1,000 segments for the bridge. 

The 1,800 piers took nine months to build and are all slightly different to support the curve of the viaduct eastward around the lakes. 

To support construction, HS2 has built a temporary factory close to the site that casts around 12 segments weekly using a match-casting technique. 

In addition, each pier has a tower crane with a temporary access bridge linking them to the construction site.

Align also used cofferdams to hold back the water while they installed the 60m deep foundations into the lake. 

On completion 

Once built, 11 will support the viaduct over the water, with 45 piers on land. 

Align will install deck segments on each side of the piers to support the construction of the half-arches. 

The viaduct will have steel tensioning cables threaded through its segments to strengthen the structure. 

HS2 will replace the factory and the buildings surrounding the viaduct with chalk grassland and woodland.

This development aligns with the programme’s ‘green corridor’ project. 

The Colne Valley Viaduct will form a key part of the HS2 route – helping to deliver better connections across the UK, free up rail capacity on the existing network, and offer passengers zero carbon travel options,” said HS2 Ltd project client David Emms. 

If you enjoyed this, check out Union Chain Bridge: A three-year engineering challenge concludes

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