A giant bridge building machine has started building a giant bridge for HS2 just inside the M25 in west London.

Launching girder (c) HS2

This is the Colne Valley Viaduct, which will be a two-mile long bridge spanning a series of lakes and waterways between Hillingdon and the M25. When completed, it will also be the longest railway bridge in the UK.

To assemble the pre-cast concrete segments that will form the bridge, a huge bridge building machine has been assembled at the north end of the viaduct and will span between the viaduct supports to drop the bridge pieces into place. Once each section is complete, the machine will inch itself forward into position to build the next stage.

Launching girder (c) HS2

56 piers each weighing around 370 tonnes are being constructed along the Colne Valley ahead of the girder, with the girder moving from one pier to the next, installing the deck segments as it goes. One segment is put in place each side of the central pier, using a cantilever approach to balance the structure, as two half-arches either side of each pier are constructed simultaneously. Steel tensioning cables will be threaded through the segments to strengthen the bridge.

Known as a ‘launching girder’, the 160m long bridge-building machine is the only one of its kind in the UK. Originally built in 2004, the launching girder was first used during the construction of the Hong Kong East Tsing Yi Viaduct. Specially designed to handle complex viaduct construction, the machine is named ‘Dominique’ in memory of Bouygues engineer Dominique Droniou who played a leading role in its design and development.

A total of one thousand deck segments will be needed, with each one weighing up to 140 tonnes. To allow for the curves of the viaduct as it crosses the valley, all the segments are slightly different shapes and made on site at a purpose-built temporary factory close to the north abutment.

In another visible sign of progress on the project, the team have also completed the construction of three of four jetties across the lakes to get equipment into position to support the construction and help take construction vehicles off local roads. Where the viaduct crosses the lakes, the piles are being bored directly into the lakebed, using a cofferdam to hold back the water while the pier is constructed.

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.

Colne Valley Viaduct (c) HS2

The viaduct project is being led by HS2’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick.


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  1. Mark Chapman says:

    What an absurd waste of public money to save 20 to 30 minutes travel time from London to Birmingham it’s already well over budget which is why they are not continuing to Manchester. This going to take years and years and the costs will continue to rise throughout the construction.the government need to think about the costs being incurred and rethink their decision.

    • ChrisC says:

      It’s not just about saving time between London and Birmingham.

      The line hugely increases rail capacity – not just for that station pair but also for more local services as well as for freight.

      It’s simply not possible to do any of that with the existing infrastructure.

    • Timothy Mallet says:

      Mark you seem to have missed the point about the West Coast mainline being at capacity and this opens up huge potential for extra trains when Express moves to HS2. This means more modular frieght, local stopping services etc. It has never been touted as only saving 20 minutes. I bet you don’t like any change and complain when the council don’t cut the grass to your liking!

  2. R kemp says:

    I would like to work on the tunnelling section when it starts any one know who will run that section how apply for a job I would appreciate it thank you

    • ianVisits says:

      It started a year ago, and if you want to work on HS2, it makes sense to look at the HS2 website for jobs.

  3. John W says:

    The article describes this new viaduct as the longest in the UK. However, with respect, the Greenwich railway brick arch viaduct (1834-36) is understood to be longer:

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