HS2 engineers have completed a forty-metre span that will form part of the high-speed rail project’s Colne Valley Viaduct on the outskirts of London.

This video includes stop-motion footage of the work:

Harefield’s Moorhall Road has now reopened after being closed for three weeks to allow HS2 to bring in cranes to lift eleven segments weighing between 115 and 130 tonnes each into position over the road. Engineers then used internal steel cabling to strengthen them.

One of the more controversial structural features of HS2, the Colne Valley Viaduct will stretch for more than two miles (3.4km) across the Grand Union Canal, River Colne, local roads and a series of lakes on the outskirts of London between Ruislip and the start of the Chiltern tunnels, making it  the longest railway bridge in the UK.

The viaduct’s widest spans – up to eighty metres long – are where it crosses the lakes, while narrower spans will be used on the approaches. HS2 chose this design to allow for views across the landscape, to minimise the impact of the viaduct on the lakes and to complement the natural surroundings. The design was inspired by the flight of a stone skipping across the water, and will see the viaduct carry the railway around ten metres above the surface of the lakes.

The viaduct is being constructed in one thousand segments, all of which are slightly different from each other because of the curve of the viaduct. All the segments are being manufactured at a temporary factory near the site, with direct access to the M25.

Usually, segments are slotted into place by a giant seven-hundred-tonne launching girder. But in this case, engineers used cranes so that they could carry out the work during the school summer holidays when there are fewer cars on the road.

Welcoming the milestone, HS2 Ltd’s Senior Project Manager, Billy Ahluwalia, said: “HS2 will transform journeys across the UK, boosting the economy and unlocking more space on our existing rail network. But it’s also important that we minimise disruption during construction.

“That’s why we brought forward construction of this span, so it could be done during the school summer holidays when we knew traffic would be lighter. It’s great to see the span complete and I’d like to thank everyone who worked so hard over the last 3-weeks to get it done.”

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

Align’s Surface Operations Director, Derek van Rensburg, said: “Having the flexibility to introduce a crane to complete the span across Moorhall Road during the summer holidays rather than using the launching girder, thereby minimising the impact on the local community, is all credit to the Align team involved, working with our supply chain partners and in particular VSL, which together delivered the work safely.”