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Artist impression of the Colne Valley Viaduct

Colne Valley viaduct

We are building a new 3.4km viaduct crossing the Colne Valley

Here you can find out more about the design and the construction of the Colne Valley Viaduct

Construction of the UK’s longest railway bridge began in early 2021, with an expert team of ground engineers sinking the first of almost 300 piles that will form the foundations for the Colne Valley Viaduct.

The viaduct, which will carry the new high-speed rail line for 3.4km across a series of lakes and waterways on the north west outskirts of London, will be almost a kilometre longer than the Forth Rail Bridge and carry trains travelling at speeds of up to 200mph.

The Colne Valley is an area of diverse countryside with areas of parks, green spaces and reservoirs. Along with the River Colne and the Grand Union Canal, the valley is a well-used public space offering recreational opportunities for visitors to enjoy.

Architect's impression images of the Colne Valley Viaduct

Set low in the landscape, the design 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.

The structure will be supported by 56 piers, with the widest spans reserved for where the viaduct crosses the lakes, and 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 the natural surroundings.

Animated fly through of the Colne Valley viaduct and Chiltern tunnel approach

Animated fly through of the Colne Valley Viaduct and Chiltern Tunnel approach

Constructing the viaduct

Over the next year, engineers from HS2 Ltd’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick – will construct 292 piles under the ground to support the viaduct piers.

On top of each group of piles – some of which will go up to 55m into the ground – a concrete pile cap will support the pier which will in turn support the full 6,000 tonne weight of the bridge structure above. Instead of hammering the piles into the ground, holes will be bored before being backfilled to create the pile. The main deck of the viaduct will be built in sections at a temporary factory nearby before being assembled from north to south.

Community engagement in Colne Valley

Community engagement in Colne Valley

Managing water in the Colne Valley area

Over the last six years, HS2 has worked closely with Affinity Water and the Environment Agency to monitor water quality and agree working methods. These will be monitored by a team of specialist engineers during construction in order to protect the natural environment.

An extensive programme of test piling has already been completed with engineers sinking 12 piles at two locations with geological and structural data from these tests fed back into the design of the viaduct. This has resulted in a 10-15% reduction in the depth of the piles and associated time and cost.

This webinar, hosted by Align and HS2 in June 2021, provided residents the opportunity to hear and ask questions about:

  • how we will preserve the aquifer during the construction of the Chiltern Tunnel
  • sourcing water for the Tunnel Boring Machines (TBM’s) and supply to our compounds
  • construction methods and mitigation for piling the Colne Valley Viaduct

You can also view or download our Water in the Chilterns and Colne Valley – Frequently Asked Questions document for information about the quality and supply of water in the Chilterns and Colne Valley during construction.

Managing water in the Colne Valley area

Managing water in the Colne Valley area

Useful links

HS2 and Align, our main works contractor, held a series of community engagement events in summer 2019 to update residents and businesses on how plans have developed for the Colne Valley Viaduct. The exhibition boards below outline:

March 2018 events

Below are the boards from the March 2018 community engagement events. The PDF exhibition boards below outline key design themes related to the following topics: