The Colne Valley Viaduct is being built near Hillingdon on the outskirts of London. It will carry high-speed trains 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.

The completion of the first V-shaped piers in the lake will allow the viaduct to curve eastward, over the water. The ‘V piers’ – each weighing 1,800t – will support a row of arches inspired by the flight of a stone skimming over the surface of the water.

The first of the V-piers for the Colne Valley Viaduct

The milestone comes one year after the launch of HS2’s ‘bridge-building machine’ (link opens in new tab). For the last year, a 700t, 160m-long launching girder – the only one of its kind in the UK - has been assembling precast concrete segments to form the first 1km of the viaduct deck along the edge of the valley.

To allow for the gentle curve of the viaduct, there are slight differences in each of the thousand segments that form the arches and deck. All are manufactured at a temporary factory set up close by, with direct access to the M25 motorway,

HS2 Ltd 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.

“I’d like to thank all those involved in getting us to this exciting stage and look forward to seeing the whole viaduct come together over the coming years.”

The viaduct project is being led by HS2’s main works contractor Align JV, which is made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick working with key suppliers including VSL, Kilnbridge, Tarmac and KVJV.

The launching girder was originally built in 2004 and was first used during the construction of the Hong Kong East Tsing Yi Viaduct. The machine is named ‘Dominique’ after Bouygues engineer Dominique Droniou who played a leading role in its design and development.

In the last year, it has installed over 300 out of the 1,000 segments required to complete the viaduct deck, installing up to three pairs of segments each day

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 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.”

The ‘ V piers’, which are designed to bear the weight of the 80m-wide arches over the lakes, are twice as large as simpler piers that carry the viaduct over land.

They are cast in place using a series of moulds. Each pier has a separate tower crane, with a temporary access bridge to provide a link to 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 of the 1,800t piers took nine months to complete. A mock-up was built off site before work began on the real piers in order to help the engineers master the complex shape of the pier. In total, 11 ‘v-piers’ will support the viaduct over water with a further 45 piers on land.

Once the piers are ready, deck segments will be placed alternately on each side, using a cantilever approach to balance the structure, as two half-arches are constructed simultaneously. Steel tensioning cables will then be threaded through the segments.