Canary Wharf Crossrail station cofferdam, London, UK: design, construction and performance

The construction of the first Crossrail station at Canary Wharf in London, UK reached a significant milestone in March 2012 when the station box was formally handed over to Crossrail for the preparation of the tunnel eyes to receive and re-launch the tunnel-boring machine. The station box is constructed in the North Dock at Canary Wharf in around 9 m of dock water. Excavation of the 265 m long, 25-30 m wide and 18 m deep station box was completed in about 12 months. This paper provides useful guidance for practising engineers on the design and construction of cofferdams' retaining walls in a dock environment. It describes the performance of the retaining structures constructed using the innovative Japanese Giken tubular pile system. Some details are also included of the site-wide dewatering undertaken to lower the groundwater in the Chalk and control it, allowing excavation into the Upnor Formation and Thanet Sand. The effects of unexploded ordnance probing on the performance of the retaining wall are described. Together with details of the laboratory tests undertaken to inform the ship impact berm design and the monitoring system used to verify the retaining wall design and comparison of the predicted and measured wall movements during excavation.