RADAR TECHNIQUES FOR INDICATING INTERNAL EROSION IN EMBANKMENT DAMS

For improved dam safety in Sweden, radar techniques have been tested for detecting anomalous zones in the central core of embankment dams and the level of the core crest. Anomalies in the core may indicate a continuing process and a greater risk of internal erosion. The level of the core crest is an essential parameter since temporary overtopping of the core has been discussed in Scandinavia as a possible way of coping with extreme floods. Detection methods of the time rate of change in soil characteristics and the exact location of the core crest and its variability would be valuable for analyses of the risk of internal erosion and planning of remedial measures. A system based on ground penetrating radar with multiple antennas has been developed partly to detect the core crest. The system operates with an accuracy significantly higher than single-antenna systems. Crosshole electromagnetic tomography supplies information on the porosity variation in the plane analyzed. In particular, time changes in porosity indicate that internal erosion is a serious problem.