Effectiveness of geoelectrical resistivity monitoring for estimation of moisture changes in the unsaturated zone of an embankment
Abstract
For prevention of disastrous slope failures, it is important to be able to monitor changes in water content within a slope in both time and space, because permeating water reduces the strength of the foundation of the slope and increases the likelihood of landslides and rock collapses. Geoelectrical monitoring using the DC resistivity method is considered to be applicable to estimating moisture changes in the unsaturated zone of a slope. In order to confirm it, we conducted the experiment of geoelectrical monitoring within the slope of an experimental embankment. Thirty-seven electrodes were placed at 0.5 m intervals along an 18-m long monitoring line that crosses the 12-m long slope. The volumetric water content and temperature have been measured at two depths of 0.2 and 0.5 m at two places along the slope. The meteorological observation by the Japan Meteorological Agency has performed at the place about 8 km away from the embankment, and our original meteorological observation has been carried out at the embankment since December 2011. Using dipole-dipole and Wenner electrode arrays, resistivity data have been collected nearly every month since February 2011. The results clearly show seasonal changes in the resistivity structure of the embankment, with resistivity becoming low in the summer wet season and high in the winter dry season. This seasonal resistivity change corresponds mainly to changes in temperature. The change in temperature-compensated resistivity is inversely proportional to the change in volumetric water content. This means that changes in water content in the embankment can be monitored by geoelectrical monitoring in conjunction with temperature correction. We also conducted continuous geoelectrical measurements for a two-week period that included an episode of heavy rain. A sudden change of the volumetric water content near the surface of the slope accompanying the rain can be detected by the resistivity change. It seems that the geoelectrical monitoring is effective for monitoring short-term changes in water content in the unsaturated zone caused by permeating precipitation. We measured the resistivity with the water content of soil samples which were acquired from this embankment before and after a heavy rain. The resistivity is well correlated with the volumetric water content, indicating that water content can be obtained from geoelectrical data quantitatively. The geoelectrical monitoring is effective for estimation of moisture changes in the unsaturated zone within the slope of an embankment.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.H53I1638T
- Keywords:
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- 1835 HYDROLOGY / Hydrogeophysics;
- 1866 HYDROLOGY / Soil moisture;
- 1875 HYDROLOGY / Vadose zone;
- 1895 HYDROLOGY / Instruments and techniques: monitoring