Abstract
Recently, the accidental collapse of structures due to natural disasters such as large earthquakes and large-scale typhoons, or local torrential rain as a result of global warming, has been regarded as a serious problem for effective and precise management of infrastructure safety. Particularly, dams as large-scale structures should be evaluated for the safety of their water sealing performance after transformation of the dam structure by strong earthquake vibrations. It is very important to establish monitoring techniques to visualize the penetration during filling of the dam for the long term. The authors conducted an electrical exploration during the first filling of a rock-fill dam site, as well as laboratory tests using samples of the materials which constitute the dam. As a result, a greatly decreased zone of resistivity (-75%) was confirmed in the rock material in the upstream side after filling. In addition, a decreased zone of resistivity (-40%) appeared in the core material area, but the zone of the resistivity change from -20 to -5% was widely distributed in the core material area and the rock material in the downstream side, except for the shallow zone. Furthermore, the resistivity of the samples of dam materials decreased to -80% when the water saturation was increased from 20% to 100% in the laboratory tests, so we can infer that water saturation is the most dominant factor affecting the resistivity of the dam materials. These results suggest that water saturation in the dam during filling can be visualized by utilizing the resistivity change. In conclusion, electrical exploration is an effective method to monitor penetration during filling of the dam, and to evaluate the safety of the dam’s water sealing performance in the event of large earthquakes in the near future.
