The Colne Valley Viaduct will stretch 3.4km across a series of lakes and waterways between Hillingdon and the M25, northwest of London.
HS2 minister Andrew Stephenson MP yesterday visited the to see the launch of the 700-tonne bridge-building machine that will be used to place the segments.
Known as a ‘launching girder’, the 160-metre long bridge-building machine is the only one of its kind in the UK and will be used to lift the concrete deck segments that form the viaduct’s arches into position. Once each section is complete, the machine will inch itself forward into position to build the next stage.
The launching girder was originally built in 2004 and was first used on the construction of Hong Kong’s East Tsing Yi viaduct. The machine is named Dominique after the Bouygues engineer Dominique Droniou who played a leading role in its design and development.
One thousand deck segments will be needed, with each one weighing up to 140 tonnes.
To allow for the gentle curves of the viaduct as it crosses the valley, all the segments are slightly different shapes and made on site in a purpose-built temporary casting yard near the north abutment.
The viaduct project is being led by Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick.
Align JV is building 56 piers along the Colne Valley, each weighing around 370 tonnes, with the girder moving from one pier to the next, installing the deck segments as it goes. One segment is put in place each side of the central pier, using a cantilever approach to balance the structure, as two half-arches either side of each pier are constructed simultaneously. Steel tensioning cables will be threaded through the segments to strengthen the bridge.
Every segment will be a slightly different shape depending on where it fits into the viaduct and the modular approach was chosen to ensure quality, safety and efficiency.
The viaduct pre-cast factory where the segments are made at the peak of construction will cast around 12 segments every week using a ‘match-casting’ technique. This approach – where each segment is poured against the previous one – should ensure that the whole deck fits properly when assembled on the piers.
Align project director Daniel Altier said: “The start of the erection of the deck segments marks the latest important milestone for Align, relating to the construction of the Colne Valley Viaduct. There has been a lot of hard work involved to get us to this point, and the achievements so far are a great example of what collaboration and excellent teamwork can deliver. I would specifically like to acknowledge the contribution from our supply chain partners – VSL, Kilnbridge, KVJV, VolkerStevin, Tarmac, Sendin and Vaughan Plant Haulage.”
In another sign of progress on the project, the team has also completed construction of three of four jetties across the lakes to get equipment into position to support the construction. Where the viaduct crosses the lakes, the piles are being bored directly into the lakebed, using a cofferdam to hold back the water while the pier is constructed.