Application of geophysical methods to dam safety assessment in Korea

Electrical resistivity methods were applied to delineate leakage pathways and to investigate the condition of core material in earth fill dams. In other to evaluate the engineering geological properties of the soil deposits, two boreholes a dam were drilled to the bedrock that exceeds the height of the dam. A large set of field tests including standard penetration test(SPT) and in-situ permeability tests were carried out along the boreholes. A series of laboratory tests were also conducted on the undisturbed soil samples obtained using the split-spoon sampler and thin wall tube sampler to determine their engineering characters. The resistivity values which were estimated from the previous inversion result for each depth were compared with the N values from SPT for each borehole. It could be classified in two groups where were not showed in general trend and most of the sites had some seepage problem and decrepit facilities need to be improved. We have also measured resistivity values of undisturbed soil samples obtained from boreholes at 311 different dam sites. We confirmed low resistivity values of soil in core material were distributed at the Gyeongsang basin and some regions in Korean peninsula. As a result of these studies, it was possible to get more quantitative interpretation of seepage problem. Key words: resistivity, leakage, earth fill dam, SPT, N value