A major milestone in the construction of what will become Britain’s longest railway bridge was achieved when HS2 engineers completed a key 40-metre span.
Work was scheduled for the school holidays last month, when traffic is light, to minimise disruption while working on the Colne Valley Viaduct.
Cranes were used to lift 11 segments weighing between 115 and 130 tonnes in to place. These were then strengthened with internal steel cabling to complete the span.
Once complete, the 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.
To allow for the gentle curve of the viaduct, each of the one thousand 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 the Moorhall Road site to allow the closure to coincide with the school summer holidays when traffic is lighter.
Billy Ahluwalia, HS2 Ltd’s senior project manager, said: “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.”
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 80 metres long, carrying the railway around 10 metres above the surface of the lakes.
Image credit: HS2
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