Quantification of Degree of Saturation at Shallow Depths of Earth Slopes Using Resistivity Imaging Technique

Earthen slopes encountered in engineering practice typically consist of unsaturated or partially saturated soils. During rainfall, water infiltrates into the slope and causes a reduction in suction. Slope stability is affected by the increase in the degree of saturation as a result of the reduction in normal stress and cohesive strength along potential failure surfaces. Therefore, to determine the geohazard potential, it is important to know the degree of saturation within slopes at shallow depths. Resistivity imaging (RI) is one of the most convenient techniques available for geohazard studies; however, only qualitative saturation profiles can be obtained using this method. Quantification of the degree of saturation has become important for using RI in the evaluation of the geohazard potential of slope failures. The objective of this study was to quantify the degrees of saturation at shallow depths using RI. Electrical resistivity tests were conducted in the laboratory on high plasticity clay (CH) and lean clay (CL) specimens, and to identify the effects of the degree of saturation and cation exchange capacity (CEC). Multiple linear regression (MLR) analyses were carried out on the laboratory resistivity test results, using statistical analysis software SAS. Two MLR models were developed that correlated electrical resistivity with the degree of saturation and CEC. RI tests were conducted on earthen slopes, and using MLR models, degrees of saturation were determined from electrical resistivity values observed at field conditions.