Geoelectrical monitoring of the slope of an embankment using a large-scale rainfall simulator

Abstract

Measuring the temporal variation of water content along a slope is important for 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). Measurements of nearsurface soil water content and temperature have been conducted at four places along the 12-m long slope. The embankment is usually outdoors and observations in natural weather have been performed. The results of the repeated geoelectrical surveys show that short-term changes in resistivity correspond to changes in water content caused by rainfall. In particular, a large shortterm increase in water content that causes a slope disaster is detectable by a decrease in resistivity. In order to confirm this, we applied artificial rain to the embankment, controlling the total amount and intensity of rainfall using the mobile simulator. 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 apparent resistivities changed significantly with a rapid change in water content, indicating that geoelectrical monitoring is effective in assessing the condition of a slope during rainfall.