The last of 292 concrete piles that form the foundations for the UK’s longest railway bridge were installed at the site of HS2’s Colne Valley Viaduct.
Once complete, the 2.1 miles (3.4km) bridge will carry the new high-speed rail line across a series of lakes and waterways near Hillingdon on the northwest outskirts of London.
The 2.1 mile (3.4km) Colne Valley Viaduct will be 100m longer than Dundee’s Tay Bridge, which currently holds the title.
The construction of the foundations, the 56 huge piers and the deck on top have all been happening in parallel – with separate teams working from north to south. Deck assembly began last year, with more than 500 meters of the viaduct structure now complete.
To deliver the 66 piles in the lakebed, 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 are also used to transport materials and equipment while constructing the piers and viaduct deck, keeping vehicles off local roads.
Click here to find out more about HS2’s longest viaduct.
Construction of the HS2 project – designed to improve rail links between London, Birmingham and North, help level up the economy and provide a low-carbon alternative to the car and air travel – is ramping up across the UK with almost 30,000 jobs now supported by the project.
“Once complete, HS2 will transform journeys across the UK, help to boost the economy and support the UK’s transition to net zero,” says HS2 Ltd’s Project Client, David Emms.
“The completion of the piling for the Colne Valley Viaduct is a major achievement for our team and marks the end of almost two years of hard work. With pier construction and deck assembly underway, the viaduct is fast becoming one of the project’s most impressive and recognisable parts,” says HS2 Ltd’s Project Client David Emms.
The viaduct is being built by HS2 Ltd’s main works contractor, Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick, working with its contractor KVJV– who spent almost two years on the piling. KVJV is a team made up of Keller Group and VSL International.
On top of each group of piles – some of which are to a depth of 60m into the ground – a concrete pile cap will support the pier, which will, in turn, support the weight of the bridge structure above. Instead of hammering the piles into the ground, holes were bored before being backfilled to create the piles.
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 that lifts each piece into position before shifting itself forward to the next pier.
“Completing the piling is a great achievement for Align and the team at KVJV, working over the lakes and waterways across the Colne Valley. We were able to complete the piling with no significant impact on the environment, a great result for the whole team,” says Align’s Surface Operations Director, Derek van Rensburg.
Set low into the landscape; the most comprehensive spans are reserved for where the viaduct crosses the lakes and narrower spans for the approaches. This design was chosen to enable views across the landscape, minimise the viaduct’s footprint on the lakes and help complement the natural surroundings.
The design was inspired by the flight of a stone skipping across the water, with a series of elegant spans, some up to 80m long, carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal.
HS2 worked closely with Affinity Water and the Environment Agency to monitor water quality and agree on working methods. A team of specialist engineers monitored these during construction to protect the natural environment.
Before work began, an extensive programme of test piling was completed with engineers sinking 12 piles at two locations, with geological and structural data from these tests fed back into the design of the viaduct. This resulted in a 10-15% reduction in the depth of the piles and associated time and cost savings.
Source: © High Speed Two Ltd 2023
Image source: © High Speed Two Ltd 2023
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