USING ELECTRICAL RESISTIVITY TO ASSESS LANDSLIDES: EXAMPLES FROM KENTUCKY AND PENNSYLVANIA

Several geophysical techniques are used to characterize landslides, and a common technique is electrical resistivity (ER). Many of the factors that influence slope movement, such as moisture and clay contents, also control electrical resistance of soils and rock. Variations in resistance to current flow cause variations in potential differences, which can provide information about the subsurface. The goal of an ER measurement is to image the subsurface resistivity distribution, which can be correlated with soil thickness, geology, structure, and moisture conditions. However, ER is seldom used as a tool to determine geotechnical conditions and assess hazard. For landslides, resistivity contrasts may reveal lateral continuity, slide planes, groundwater concentrations and changes, or clays. ER was measured at three landslides, two in Kentucky and one in Pittsburgh, Pa. Each landslide had different geologic settings, soil types, and slope histories. Methodology included measuring and imaging two-dimensional surface electrical-resistivity arrays at each landslide. Integrating multiple ER array configurations and electrode spacings, in conjunction with mapping of observed surface features, proved an effective way to characterize slope failure. For the two slides in Kentucky, correlations were made with electrical data and in-situ hydrologic parameters, and then modeled to demonstrate that ER can be a tool to assess shear strength. The practical application of this study demonstrates that nonintrusive, repeatable electrical-resistivity measurements can be used to investigate landslide type, failure zones, and areas of variable moisture content, but also be correlated to rock and soil properties for effective geotechnical investigations.