The 3.4km Colne Valley Viaduct, in the northwest London commuter heartlands, is mostly being built by a launching gantry that slides along progressively placing precast deck segments.
However, for a 40-metre section that crosses over a public highway – Moorhall Road in the Harefield – cranes were preferred. That span was completed last week, bringing to an end a three-week road closure. A timne lapse video showing the work has now been released (below).
Timed for the school summer holidays to reduce disruption for the community, the closure allowed HS2 to bring in cranes to lift eleven 115- to 130-tonne segments into position over the road. These were then reinforced 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 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, within Align’s huge site compound, with direct access to the M25.
Most of these segments are slotted into place by a 700-tonne launching girder. 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.
The viaduct is being built by Align JV, comprising Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
Align 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.”