HS2 has started work on the first of 56 giant concrete piers that will support the UK’s longest rail bridge as it prepares to start tunnelling work in London
The Colne Valley Viaduct will stretch for 3.4km over a series of lakes, carrying 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 HS2’s main works contractor Align JV – Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick – working in partnership with Kilnbridge.
The 6m tall reinforced concrete pier weighed 370 tonnes
Weighing around 370 tonnes, 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.
Viaduct design was inspired by a stone skipping across the water
The design of the viaduct was inspired by the flight of a stone skipping across the water, with spans up to 80m long carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal.
Main viaduct deck will be built in a factory before being assembled
The main deck of the viaduct, which support the railway line, will be built in 1,000 separate unique segments at a temporary factory before being assembled from north to south.
First giant tunnel boring machines delivered to HS2’s West Ruislip site
Work on the viaduct got underway as the first two giant tunnel boring machines were delivered to HS2’s West Ruislip site ahead of tunnelling work getting underway in London.
The 1,900-tonne machines were delivered to HS2’s main work’s civils contractor, Skanska Costain STRABAG joint venture (SCS JV) in November from international specialist TBM manufacturer Herrenknecht in Germany.
6 TBMs will bore 13 miles of twin bored tunnels underneath London
The two machines will be the first of six TBMs that will bore 13 miles of twin bored tunnels underneath London where HS2 services will run. They will join eight other machines that will operate on Phase One of the HS2 project between London and the West Midlands, which will dig 64 miles of tunnels in total.
The two machines have been designed specifically to bore predominantly through Lambeth group (a set of geological rock strata), chalk and London clay, and are automated to install 4,220 tunnel segment rings each, to create each five-mile tunnel.
15 people will work around the clock to operate each TBM for 2 years
Around 15 people at a time will operate on each TBM working in shifts, keeping the machines working around the clock for two years, only stopping at Christmas and Easter. A team of approximately 40 people are working to assemble the TBMs, preparing for the launch later this year.
James Richardson, managing director of Skanska Costain STRABAG joint venture, said: “Delivering these huge TBMs to West Ruislip was an enormous logistical challenge involving 260 deliveries, including 110 abnormal loads. Our team worked tirelessly to deliver these items efficiently, while minimising disruption to our neighbours. All eyes will be on West Ruislip in 2022 as we start to build the London tunnels, reaching depths of 30m below ground.”
