Assessing the integrity of spillway foundations

The erosion under a spillway can be a long-term issue that threatens the structural integrity of a water reservoir. The spillways under investigation were suspected to be defective after they had been commissioned in 1987 and 1939, respectively. Potholes and subsurface cavities were confirmed in the safety assessment using various NDT techniques including ground penetrating radar and impact echo. The GPR inspection was able to differentiate the intact region from the cavities under concrete slabs. The impact echo results and associated analyses provided further evidence of inferior condition in the soil under the concrete slabs. The engineering team designed and executed the repair projects based on the conclusion of the integrity assessment. Repetitive GPR scans were also carried out after the rehabilitation of spillways. Not only the quality of repair can be evaluated, the scans also provided a baseline record for long-term condition assessment of the spillway and the reservoir in the future.