Construction of HS2’s long Colne Valley railway viaduct in west London has reached the halfway mark, with the railway deck now assembled on 28 of the supporting piers.
Construction of its 56 piers to carry the deck across land and water began in December 2021. For the past 18 months, a massive launching girder has been working its way south across the valley, one pier to the next, to lower and fix into place the viaduct’s deck segments.
Weighing up to 140 tonnes each, more than 500 of the Colne Valley Viaduct’s 1,000 deck segments have now been installed.
Each one is uniquely shaped to enable the structure to curve gently as it carries the railway for just over 2 miles over land, lakes and the Grand Union Canal.
To assemble the piers that the railway deck sits on, the team first had to construct over a kilometre of temporary jetties, with cofferdams to hold back the water around each set of foundations. The jetties also transport materials and equipment while constructing the piers and viaduct deck, keeping vehicles off local roads.
The main deck of the viaduct is being built in 1,000 separate segments at a temporary factory nearby and assembled using a bridge-building machine, which lifts each piece into position before shifting itself forward to the next pier. Once the piers are ready, deck segments are placed alternately on each side, using a cantilever approach to balance the structure, as two half-arches are constructed simultaneously. Steel tensioning cables are then threaded through the segments to strengthen the bridge.
Sir Jon Thompson, HS2’s Executive Chair, said: “HS2 is by far the biggest and most ambitious infrastructure project in the UK and it’s fantastic to see phenomenal feats of civil engineering like the Colne Valley Viaduct taking shape. The enormous progress made in the last three years along the length of the route between London and the West Midlands is testament to the skill and dedication of the thousands of people who work on this transformational project every day.”
The Colne Valley Viaduct construction is led by HS2’s main civil works contractor, Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick.