Enormous HS2 parts factory built for UK’s longest railway bridge

Enormous HS2 parts factory built for UK’s longest railway bridge

A huge new temporary factory has been opened near the M25 in Greater London, specifically to construct parts of the UK’s longest railway bridge – all part of the HS2 infrastructure project.

The mega factory has been specially constructed to produce the deck segments for the Colne Valley Viaduct.


Once complete, the viaduct will become the UK’s longest railway bridge at 2.1 miles. It will carry HS2 trains over a series of waterways and lakes across the Colne Valley just outside London. Passengers will be transported at high speed over the River Colne and the Grand Union Canal in North London.

The inspiration for the viaduct’s design is the flight of a stone skipping over water.  It will consist of a number of elegant arches up to 80 metres long, around 10 metres above the landscape below.


First huge deck segments to roll off the production line


The temporary factory is 100 metres long and has an internal volume of 105,000 cubic metres, making it larger than the Royal Albert Hall. It has been designed to create around 12 of the 1,000 enormous deck segments every week, using a ‘match-casting technique’. This involves pouring each modular segment against the previous one, ensuring a perfect fit across the whole arch when re-assembled on site.


Production of the segments, which are each larger than a double decker bus and weighing up to 140 tonnes, has already begun.


Once the viaduct construction project is complete, the modular segment casting factory will be dismantled. All trace of it and surrounding buildings will be removed, and the plan is to turn the whole area into a ‘green corridor’ for HS2. This involves a transformation of the space between the Colne Valley Viaduct and the Chiltern Tunnel into an area of chalk grassland and woodland.


The Colne Valley Viaduct project is led by principal HS2 contractor Align JV, which is made up of experts from VolkerFitzpatrick, Sir Robert McAlpine and Bouygues Travaux Publics.


Project director at Align JV, Daniel Altier commented on the opening of the new factory:


“Seeing the first deck segments being cast in the factory marks a significant milestone for the project. 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.”


Construction progress over in the Colne Valley


While the production line at the new mega factory ramps up, the Colne Valley Viaduct site itself is a hive of construction activity. Foundation work was started earlier in 2022, involving the construction of nearly 300 piles and 56 pile caps across the whole length of the viaduct.


The first two jetties have also been constructed across the lakes. A total of four will eventually be needed to get all equipment in place to support the construction.


Another key element of the project is also underway – the 56 hefty piers that will support the weight of the viaduct. Each weighs around 370 tonnes and sits on the concrete piles below.


Dream of working on some of the UK’s most exciting infrastructure and civil engineering projects? Find your next role with VGC Group.