Thames Tideway Tunnel: Blackfriars Bridge Foreshore: Innovative In-river Construction
This paper details the complex engineering and collaborative innovation behind the construction of the Fleet Main combined sewer overflow (CSO) interception culvert at the Blackfriars Bridge Foreshore site, part of the wider Thames Tideway Tunnel programme. Due to severe spatial constraints, including a listed Victorian bridge, critical underground infrastructure, and shallow tunnels, traditional in-situ construction was unfeasible.
The team devised a novel approach: a 96-metre-long precast concrete culvert, constructed within a cofferdam and floated into final position beneath a bridge arch. Extensive physical and finite element modelling informed the culvert’s buoyancy, stability, and set-down process, supported by scaled hydraulic trials and rigorous flotation testing. A two-stage float-out operation, timed with tidal cycles, was successfully completed over a single weekend in 2020.
Post-installation, the structure was sealed, integrated with the main tunnel, and complemented by the creation of a permanent riverside public space. This solution not only prevented over half a million cubic metres of untreated sewage from entering the Thames annually, but also enabled wider catchment benefits and demonstrated how engineering ingenuity can overcome extreme urban constraints.
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This paper appeared in the Proceedings of the Institution of Civil Engineers – Civil Engineering, the flagship journal of the Institution of Civil Engineers, published by Emerald Publishing Limited.
Image credit: Tideway