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The first in line

The Isle of Dogs station will be one of the first to be built on the Crossrail network. As with other work along the line, it will bring huge challenges.

More than 90,000 people work at Canary Wharf, rivalling the Square Mile for the financial heart of London. The tallest building in the UK, One Canada Square (235m), and the cluster of brassy skyscrapers are the closest thing we have to the iconic city skyline of New York. It’s fitting, then, that the place which brought the banking world into the 21st century – at least in property terms – will be connected to the development that will bring London’s infrastructure into the 21st century.

Click here to view Isle of Dogs station works

"When Crossrail was revived in 2001, the Jubilee line had been open for 18 months and the development had expanded," says Canary Wharf Group transport adviser Jim Berry, who is also responsible for working with the Crossrail design team on this element. "It was natural that Crossrail should come to Canary Wharf. "It’s positive not only for this area but also the East End [of London]. It improves the level of accessibility and travel times will be reduced dramatically, and it will also support future growth and support growth for housing to the east," adds Berry.

Click here for Isle of Dogs Crossrail station cross section

Canary Wharf Contractors (CWC) will be building a large part of the new station for Canary Wharf Group, of which it is a subsidiary. CWC will provide the shell and core (for the station) and interfacing with the rail infrastructure as it comes through. The shell of the basement needs to be in place by the time the Crossrail tunnel boring machines (TBMs) hit Canary Wharf in about four years. This will happen as they progress from the starting point at the Limmo peninsula (in the area of Canning Town) and work westwards towards Farringdon. "The size of the project is something we’re quite happy to undertake, but the challenge is building it in time," admits CWC operations executive Michael Bryant.

Although the station is just one part of the overall Crossrail scheme, it is a huge project in its own right. It will take the form of a 260m-long box – as long as the tallest building at Canary Wharf. "The station [design] is like a long thin building on its side, underwater," says Bryant. "Canary Wharf is good at building tall buildings. It’s big, but the magnitude doesn’t hold any mysteries for us."

The box is between 27m and 30m wide and is six storeys high. Four of these storeys will be underwater or underground as the station is being built in the north dock of West India Quay in Canary Wharf. The bottom floor of the station will be the platform level, around 22m below water level and 13m below the dock bed. Above this will be a concourse level, two levels of retail, followed by two further retail levels above water and a man-made landscaped park level. The top of the box is finished off by a wooden lattice structure with ETFE cladding to allow light into the area.

Because of the dock, a cofferdam will be built to create a dry area to work in and to allow the working dock to continue operations. This involves using 1.2m-diameter steel tube piles that have channels along their side which can interlock to form a watertight wall. However, these steel piles can only go as far as the top of the Crossrail tunnel. If the TBMs had to bore through steel, the expensive equipment could be damaged. An auger is sent down inside piles into the bedrock below and contiguous piles cast to form the lower station walls. "The steel piles go 6m into the dock bottom," says Bryant. "It was a balance between keeping it high enough for the tunnel boring machine and socketing it in enough into impermeable layer [to make it watertight] and to give enough stability."

Not only does CWC have around 9m of water pressure from the docks to worry about, but the basement construction will also cut through a layer of clay below the dock bottom, where groundwater is trapped. Work has already started on lowering the water table and will continue for three years. A concrete wall will be built inside the tubular cofferdam to create the permanent box. The integrated structure will then be able to take the pressure from the dock water and the groundwater when the dewatering is stopped. Final planning permission is expected by the end of the year and work on site is due to begin in January.

Crossrail is finally here. "I think Crossrail is one of the great projects, like the Paris RER, which has taken a long time to get here, but it’s important that it gets built," says Berry. "Great things will happen once it’s done."

Better access for all
Improving access into Canary Wharf isn’t the only benefit the Isle of Dogs Crossrail station will bring. It will also improve access around the area as a whole.

The docks add charm, but they also isolate Canary Wharf and make it harder to move around. The new station nestled in the bustling Canary Wharf development to the south and the residential area to the north will also make it easier to get around. "We will be using the station to create a bridge between us and the community," says Canary Wharf Group transport adviser Jim Berry. "The docks, to some extent, separate us from the surrounding area. The station includes three bridges on each side of the development."

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