A non-destructive testing (NDT) method was used in a concrete face rockfill dam (CFRD)\nto identify the condition of the concrete face slab and detect any existing cavities between the concrete\nface slab and the underlying support layer. The NDT for the concrete face slab was conducted\nusing the impulse response (IR) method and the electrical resistivity tomography (ERT) method\nwith the application of non-destructive electrodes. Information regarding the dynamic stiffness and\naverage mobility of the concrete was obtained based on the mobility-frequency of the IR method, and\ncavity detection under the plate structures was analyzed using the two-dimensional (2D) electrical\nresistivity section of the ERT method. The results of the IR method showed that zones with low\ndynamic stiffness and high average mobility were expected to be found in concrete of poor quality\nand in cavities beneath the concrete face slab. The results of the ERT method showed that zones\nwith high resistivity were expected to be cavities between the concrete face slab and the underlying\nsupport layer. As a result, the tendency toward low dynamic stiffness, high average mobility, and\nhigh resistivity in both methods implies unstable concrete conditions and the possible occurrence of\na cavity. The results of the two methods also showed a good correlation, and it was confirmed that\nthe NDT method was reliable in terms of cavity estimation.
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