HS2 has made further progress on the UK’s longest railway bridge following the completion of the first piers that will carry the viaduct over a series of lakes just outside London.
The Colne Valley Viaduct – which is being built near Hillingdon – will carry high-speed trains more than two miles (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.
For the last year, a 700-tonne ‘launch girder’ – the only one of its kind in the UK – has been assembling large pre-cast concrete segments to form the first 1 km of the viaduct deck along the edge of the valley.
Now, the first v-shaped piers have been installed in the lake to allow the viaduct to curve eastward over the water.
The ‘v-piers’ – each weighing 1,800 tonnes – will support a row of arches inspired by the flight of a stone skimming over the surface of the water.
To allow for the gentle curve of the viaduct, HS2 says each of the one thousand segments that form the arches and deck are slightly different.
Each segment has been manufactured at a nearby temporary factory that has direct access to the M25.
HS2 project client David Emms said: “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.
“That’s why it’s great to see so much progress over the last 12 months and especially the completion of the piers that will allow the girder to head out over the lakes later this year.”
Known as a ‘launching girder’, the 160-metre-long bridge-building machine is used to lift the giant concrete deck segments that form the viaduct’s arches into position.
Once each section is complete, the machine inches itself forward to build the next stage.
The viaduct project is being led by HS2’s main works contractor, Align JV, a team comprising Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
Align project director Daniel Altier said: “I am delighted that by working as an integrated team with our supply chain partners, we have been able to erect nearly a third of the deck and complete the first v-pier, just a year since Dominique [the launching girder] starting operating.
“What has been achieved would not have been possible without the support of the different teams across the project – including Quality, Lifting, Safety, Consents, Environment, Surveying, and also Earthworks – for maintaining the haul road on which the 60-140 tonne segments are transported from our factory to meet the girder.”
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Designed to bear the weight of the 80m wide arches over the lakes, the v-piers are twice as large as simpler piers that carry the viaduct over land.
Cast in place using a series of giant moulds, each pier has a separate tower crane, with a temporary access bridge linking them with the main construction site.
Cofferdams were used to hold back the water while the 60m deep foundations were built into the bed of the lakes.
Each pier weighs around 1,800 tonnes and took nine months to complete.
In total, 11 v-piers will support the viaduct over water with a further 45 piers on land.
Image: A HS2 v-pier being constructed at the Colne Valley Viaduct
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