The Colne Valley Viaduct is being built to carry the HS2 high-speed line across a series of lakes and waterways outside Hillingdon. The first 480m have been built over the last seven months using a 700t ‘bridge-building machine’.

The Colne Valley Viaduct is being built by a 700t 'bridge-building machine'

Huw MerrimanThe UK government’s rail minister, Huw Merriman (left), has visited to the site and officially became the first person to walk on top of the structure. He said: “This is an extraordinary feat of engineering and architecture, designed to enable spectacular views across a beautiful part of our British countryside which is being preserved and protected by this project.

“It was incredible to be the first person to officially walk on top of it today – another milestone for this monumental project which will transform journeys for people up and down the country, creating almost 30,000 jobs and providing a low-carbon alternative to cars for decades to come.”

The 160m-long ‘launching girder’ is the only one of its kind operating in the UK and is used to lift the concrete deck segments that form the viaduct’s arches. Once each section is complete, the machine inches itself forward to build the next stage.

The first 141 - out of a thousand - deck segments are now in position, with each one weighing up to 140t. To allow for the gentle curves of the viaduct as it crosses the valley, all the segments are slightly different shapes and are made on site at a purpose-built temporary factory close to the north abutment.

The viaduct project is being led by HS2’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick.

Huw Merriman on the Colne Valley Viaduct

Above: Huw Merriman

The launching girder was originally built in 2004 and was first used during the construction of the Hong Kong East Tsing Yi Viaduct.

Align project director, Daniel Altier, said: “The team at Align, along with supply-chain partners VSL, Kilnbridge, KVJV, VolkerStevin, Tarmac, Sendin and Vaughan Plant Haulage, have worked incredibly hard to get us to this point. They have demonstrated exceptional teamwork and expertise and I’m incredibly proud of what they have achieved so far. In particular, the successful completion of the A412 crossing which involved collaboration with multiple stakeholders to minimise disruption to our local community.”

Ahead of the girder, 56 piers - each weighing about 370t - are being constructed along the Colne Valley. Segments are placed alternately on each side of the pier, using a cantilever approach to balance the structure, as two half-arches are constructed simultaneously. Steel tensioning cables are then threaded through the segments.

The precasting factory uses match-casting to ensure the whole deck fits perfectly when assembled on the piers. Up to 12 segments a week can be cast at the 100m-long factory.

The design of the Colne Valley Viaduct was inspired by the flight of a stone skipping across the water, with a series of spans, some up to 80m long, carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal.

The HS2 project is designed to improve rail links between London, Birmingham and the north, help level-up the economy and provide a low-carbon alternative to car and air travel. Construction is ramping up across the UK with almost 30,000 jobs now supported by the project.