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Colne Valley Viaduct concepts created for HS2 by Grimshaw Architects
Colne Valley Viaduct concepts created for HS2 by Grimshaw Architects

Colne Valley viaduct

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

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. 

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.

Colne Valley Viaduct visualisation

The Colne Valley Viaduct will be the longest in Britain.

Constructing the viaduct

Engineers from HS2 Ltd’s main works contractor are constructing and installing 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. 

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 savings. 

Engaging on the design of the Colne Valley Viaduct

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 provide a detailed summary of how we have listened to and incorporated your feedback into the design.