Canning Town Flyover, Crossrail C305

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Challenge

The Canning Town flyover is a 330m ‘S’ shaped span viaduct completed in 2009 that carries the Docklands Light Railway. C305 is the contract covering eastern running tunnels, comprising Limmo Peninsula to Farringdon, Limmo Peninsula to Victoria Dock and Stepney Green to Pudding Mill Lane; the tunnels pass under the Canning Town flyover.

Mabey worked with client Dragados Sisk JV and project stakeholders Crossrail, Transport for London, Docklands Light Railway, London Underground and Newham Council to design and execute a complex and highly accurate settlement mitigation system for the flyover. The viaduct was designed to avoid conflict between the proposed tunnels and the viaduct bored pile foundations; the design also considered that the effects of the tunnelling would be mitigated by the installation of a live viaduct jacking scheme to control inter-pier differential settlements to within 2mm and accommodate tilt and horizontal movements of the piers.

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Solution

The viaduct was ‘floated’ on hydraulic jacks at each bearing location between and including piers NP6 and SA0 (11 piers in total). The permanent bearings were removed and temporary articulation was designed using structural steel and hydraulics. The jacks were linked and centrally operated to provide the ability to control the vertical and horizontal movement of the deck, ensuring that it remained within tolerance to a dynamic multi-linear reference plain.

The measurement of the viaduct’s position and performance was achieved through the unique combination of measuring devices and techniques linked together using bespoke software to provide accuracies of greater than 0.3mm. Data from the sensors was conditioned through a series of calculations and presented to the engineering team through LIVEsite, Mabey's exclusive web interface.

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Result

The jacking system was installed from April to May with the viaduct being floated on the system in early June. The tunnel boring machine passed under the viaduct in July on the southbound drive. The total settlement at the southern abutment was 15mm and the twist induced was always maintained within tolerance.

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