HS2 main works contractor Align JV has started work on the first of 56 concrete piers that will support the Colne Valley Viaduct as it crosses a series of lakes on the outskirts of London.
Stretching for 3.4km, the viaduct – being built as part of the High Speed 2 (HS2) rail scheme – will carry high speed trains between the outskirts of Hillingdon and the M25 on their way to Birmingham and the north.
The first pier was cast by engineers from Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine and Volker Fitzpatrick – and working in partnership with Kilnbridge.
Weighing in at around 370t, the 6m tall reinforced concrete pier was cast on site by a team of engineers who used a specially designed formwork to create the shape of the structure. This was then removed after four days to reveal the final product.
Each pier is designed to support the full weight of the deck above and rests on a set of concrete piles going up to 55m into the ground.
This foundation work began earlier this year and will require the construction of 292 piles and 56 pile caps across the whole length of the viaduct.
The team has also completed the construction of the first of four jetties across the lakes to get equipment into position to support the construction.
Where the viaduct crosses the lake, the piles will be bored directly into the lakebed, using a cofferdam to hold back the water while the pier is constructed.
Align project director Daniel Altier said: “I have no doubt that the viaduct will become one, if not the most striking element of HS2 phase one once complete. The way it will be constructed is going to be equally fascinating for engineers young and old.
“The sections for the deck will be fabricated at our main construction site to the west of London just inside the M25, and using a huge launching girder, the deck will be formed from north to south, along the line of the route, thereby keeping unnecessary construction traffic off the roads.
“I would like to thank the whole team, including our supply chain partners, who have worked very hard to enable us to meet this important milestone in the viaduct’s construction.”
The design of the Colne Valley Viaduct will carry the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal, with some of spans reaching up to 80m long.
The main deck of the viaduct – which supports the railway line - will be built in 1,000 separate segments at a temporary factory nearby before being assembled from north to south, starting next year.
As part of a push across the whole HS2 project to cut carbon in construction, the design and construction teams have also worked on cutting the amount of embedded carbon in the viaduct by around a third, by narrowing the width of the structure and applying lessons from the design of high speed railway bridges in Europe.
Over the last six years, HS2 Ltd said it had worked closely with Affinity Water and the Environment Agency to monitor water quality and agree working methods. These are being monitored by a team of specialist engineers during construction.
At the recent Tunnelling Festival conference, HS2 senior project manager Mark Clapp told delegates that both of Align’s tunnel boring machines are running ahead of schedule.
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