Geoelectrical Monitoring for Observation of Changes in Water Content in the Slope of an Embankment Caused By Heavy Rain Using a Large-Scale Rainfall Simulator

Measuring the temporal variation of water content along a slope is important for predicting and preventing slope disasters. We conducted repeated monthly geoelectrical surveys since February 2011 on one slope of an embankment in the large-scale rainfall simulator of the National Research Institute for Earth Science and Disaster Prevention (NIED). In order to confirm the relationship between water content and resistivity changes in the slope due to heavy rain, we conducted seven artificial rain experiments at the embankment, controlling the total amount and intensity of rainfall using the mobile rainfall simulator. We observed soil water content and conducted geoelectrical measurements on the slope of the embankment before, during and after the artificial rains. It is difficult to obtain the rapid change of resistivity structure due to the rain because the analysis of resistivity structure requires measurement by much electrode array combination. Therefore, we performed only a continuous measurement using a Wenner array with "a" spacing of 0.5 m and 1 m. The changes in analyzed resistivity took place almost simultaneously with changes in water content. The fall of resistivity accelerates as the intensity of rainfall increases. The resistivity changed significantly with a rapid change in water content. The change in resistivity is slightly earlier than the change in volumetric water content at the same depth. These facts indicate that geoelectrical monitoring is effective for observing changes in the water content of the slope of an embankment caused by heavy rain.