HS2 completes key Colne Valley Viaduct span

Colne Valley Viaduct, which once complete, will be the longest railway bridge in the UK.

Harefield’s Moorhall Road has reopened after HS2 engineers completed a key 40-metre span that will form part of the high-speed rail project’s record-breaking Colne Valley Viaduct.

Timed for the school summer holidays to reduce disruption for the community, the closure allowed HS2 to safely bring in cranes to lift eleven 115-130-tonne segments into position over the road. These were then strengthened with internal steel cabling to complete the span.

Once complete, the viaduct will be the longest railway bridge in the UK, stretching 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.

To allow for the gentle curve of the viaduct, each of the 1,000 segments that form the arches and deck are slightly different – and all are manufactured at a temporary factory set up close by, with direct access to the M25.

Most of these segments are slotted into place by a giant 700-tonne ‘launching girder’ – the only one of its kind in the UK. But the engineers used a different approach at Moorhall Road to allow the closure to coincide with the school summer holidays when traffic is lighter. 

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 three 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.”

Set low into the landscape, the widest spans are reserved for where the viaduct crosses the lakes, with 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 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.

The road reopened on Friday.  

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