Case Study: Wandsworth Bridge (February, 2019)
Richmond and Wandsworth Council commissioned Zetica to investigate Wandsworth Bridge, London, UK for any evidence of water penetration and retention between the carriageway surface and the bridge deck.
Our solution combined a multichannel, stepped-frequency dense array and a 4-channel impulse ground penetrating radar (GPR) system. These complimentary technologies allowed us to harness their strengths to bring about the required data with a high level of accuracy and certainty in our interpretations.
Our interpretation methodology was based on the principle that areas where water is trapped at an interface between two pavement layers will result in a higher amplitude reflection compared to areas where the interface is dry and the two materials are well bonded.
The impulse system would be used to interpret the pavement and bridge construction layers and to map the relative amplitude of observed layer interfaces. The stepped-frequency array would be used interpret and map anomalous responses in three dimensions, including buried utility services and other detectable below ground features.
The stepped-frequency dense array data identified a large amount of anomalies, structural features and buried utilities. A selection of examples are shown in the images opposite, including (top left) a buried utility running parallel to the road, (top right) a manhole chamber, (bottom left and inset) a surface crack and (bottom right) an expansion joint.