Canary Wharf Crossrail Station

Canary Wharf was the first Crossrail station to be built and the only one to be constructed over water; it is located in the North Dock of West India Quay in Canary Wharf. The base slab of the station is approximately 26m below water level. The first stage of construction involved building a cofferdam to retain the dock water on three sides. This included the installation of approximately 350 linear metres of 1.2m diameter, 18m-long steel tubes with interlocking clutches installed using hydraulic jacking techniques to create a watertight cofferdam within the dock. The works were carried out in close proximity to office buildings and residential blocks, requiring the use of techniques minimising noise and vibration. The steel tubes forming the cofferdam wall were then drilled out to a depth of 36m using rotary augered piling rigs and completed with reinforced concrete. An external restraint system using piles and beams, connected to the wall outside the cofferdam footprint, provided a free-space internal construction zone to allow for efficient station box construction.

After the cofferdam had been dewatered, stage two of piling works commenced. Utilising up to five piling rigs at peak, this included the installation of 2100mm diameter piles drilled to approximately 40m below dock bed level. These piles included heavy column sections plunged into the concrete to allow the station to be formed using 'top-down' techniques. In addition, 1200mm diameter piles were drilled to approximately 40m below dock bed level to act in tension below the base slab. All piles extend below the Thanet Sand into the underlying Chalk, drilled using bentonite support fluid. To complete the perimeter wall on all elevations, a secant wall was formed using 1200mm diameter piles founding in the Thanet Sand, installed adjacent to the existing dock wall to protect the basement from water ingress travelling beneath this existing feature.