Construction of what will be the UK’s longest railway bridge has taken a step forward as the casting of the first of 56 concrete piers has been completed.
Stretching for 3.4km, the viaduct will carry HS2 trains over the Colne Valley on a short overground stretch between West Ruislip and the tunnel mouth next to the M25 motorway. Set low into the landscape, wid spans will carry the viaduct crosses the lakes, and narrow spans will be for the approaches.
Weighing in at around 370 tonnes, the first of the 6m tall reinforced concrete piers were 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 4 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 have also completed the construction of the first of four jetties across the lakes to get equipment into position to support the construction thereby removing construction vehicles from local roads. 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.
The main deck of the viaduct – which supports the railway line – will be built in 1,000 segments at a temporary factory nearby before being assembled from north to south, starting next year.
Just 55 more piers to go.
When completed, at 3.4km long, it will be longer than the Forth Rail Bridge.