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HS2 minister Huw Merriman became the first person to officially walk on top of the UK’s longest railway bridge, which is under construction at an HS2 site just outside London.


Construction of the HS2 project, which 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, is ramping up across the UK with almost 30,000 jobs now supported by the project.

The first 480m of the Colne Valley Viaduct – which will eventually stretch for more than two miles (3.4km) across a series of lakes and waterways outside Hillingdon – have been built over the last seven months using an enormous 700 tonne ‘bridge-building machine’.

Known as a ‘launching girder’, the 160m long bridge-building machine is the only one of its kind operating in the UK and is used to lift the giant concrete deck segments that form the viaduct’s arches into position. Once each section is complete, the machine inches itself forward to build the next stage. Originally built in 2004, the launching girder was first used during the construction of the Hong Kong East Tsing Yi Viaduct. 

56 piers each weighing around 370 tonnes are being constructed along the Colne Valley ahead of the girder, with the machine moving from one pier to the next, installing the deck segments as it goes. 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.

The viaduct pre-cast factory where the one thousand segments are made uses a ‘match-casting’ technique. This approach - where each segment is poured against the previous one - will ensure the whole deck fits perfectly when assembled on the piers. Up to 12 segments a week can be cast at the mammoth 100 m-long factory, which has an internal volume of 105,000 cubic metres – making it larger than the Royal Albert Hall.

Once construction is complete, the factory and surrounding buildings will be removed and the whole area between the viaduct and the Chiltern tunnel will be transformed into an area of chalk grassland and woodland as part of HS2’s ‘green corridor’ project.

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