Field Observation of the Unsaturated Characteristics in a Mine Waste Dump During Rainfall

Field monitoring sensors and an instrumentation system were installed in a mine waste dump slope at the Imgi mine in South Korea to investigate and analyze the surficial seepage and unsaturated soil behavior at the vadose zone. The field instrumentation consisted of a data acquisition system, a solar charging system, and measuring sensors. The rainfall, matric suction, and volumetric water contents were continuously measured from the units in the site and analyzed with the soil water characteristic curve (SWCC) estimated from laboratory experiments. The variations in matric suction and volumetric water content were primarily affected by the rainfall intensity. At the surface of the waste dump slope, the largest increase and decrease in the changes of matric suction and volumetric water content were observed during the wetting and drying processes, respectively. The measured matric suction and volumetric water content data from the field monitoring site were compared with the SWCCs obtained from the laboratory test, and the measured data was located between the drying and wetting paths. The drying and wetting paths obtained from the laboratory test are regarded as the primary drying and wetting curves, respectively. Therefore, the measured data with a nonlinear relationship between matric suction and volumetric water content could be defined as scanning curves, which are located near the primary drying and wetting curves. In particular, the characteristics of unsaturated soil near ground surface were dominantly associated with the primary wetting curve.