UK: Construction of High Speed 2’s Colne Valley Viaduct, being constructed close to the village of Denham in Buckinghamshire, has reached a key milestone, with the installation of the final bridge segment on September 5.
The 3·4 km long viaduct, which project promoter HS2 Ltd claims is Britain’s longest bridge, stretches from the M25 motorway, close to West Hyde, to Harvil Road, northwest of Ickenham. The structure crosses a series of lakes and waterways within the Colne Valley nature reserve, as well as the A412 main road and the Grand Union Canal.
The Align joint venture of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick, began work on the viaduct in 2021 when the first of 300 foundation piles for the piers were sunk.
Construction of the deck started in May 2022, when the launching girder christened Dominique installed the first segment. The name was chosen to commemorate Bouygues engineer Dominique Droniou who played a leading role in its design.
The bridge deck has been constructed using 1 000 precast concrete segments ranging from 60 to 140 tonnes. The segments were manufactured by Align JV close to the northern abutment in a purpose-built factory. The factory had direct access to the M25 motorway, which reduced the number of construction vehicles using local roads. A haul road, which included pontoon bridge sections was also built to aid the assembly of the 56 piers.
The design of the viaduct incorporates two different types of piers, with a conventional vertical designed used for sections on land. Over the various lakes and watercourses, V-shaped piers were built, weighing 370 tonnes each. The V-shaped piers and segments work together to give the viaduct the appearance of the railway ‘skipping’ across the water.
Specially designed moulds were used to construct the piers, which were erected in situ, with reinforcing steel and concrete transported to each pier site via the haul road and pontoon bridges. Construction of the piers ran in parallel with the assembly of the deck, with teams working two or three piers ahead of the launching girder.
The 700-tonne girder was used to lift and install up to two bridge segments at a time. This was an essential feature, as each pair of segments had to be post-tensioned together because assembly of the deck worked outwards from the piers. This meant that during construction, each deck span was in effect a post-tension cantilever structure. However, once each span was complete and tensioned, the structure became a standard concrete box girder.
While installation of the final segment is a key milestone, the viaduct is far from finished, with installation of concrete parapets and sound barriers ongoing.
Slab track modules, rails and power and telecoms systems will follow once HS2 Ltd has let the railway systems contract for this section of the 190 km route. The contract is expected to be let by the end of 2024.
