Analyses on variations in the unsaturated characteristics of a mine waste-dump slope during rainfall

Field measurement units and a system were constructed and installed in a waste-dump slope at the Imgi mine to investigate and analyze the variations in the unsaturated characteristics of the soil. The field instrumentation system was composed of a data acquisition system, a solar system, and measuring sensors. The rainfall, matric suction, and volumetric water contents were continuously measured from the units in the instrumented 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 slope, the largest increase and decrease in the changes in matric suction and volumetric water content were observed during the wetting and drying processes, respectively. The matric suction and volumetric water content measured from the instrumented area were compared with the SWCCs obtained from the laboratory test, and the measured data were located between the drying and wetting paths. The drying and wetting paths obtained from the laboratory test are regarded as primary drying and wetting curves, respectively. Therefore, the measured data can be defined as scanning curves, which are located between primary drying and wetting curves. The variations in matric suction according to volumetric water content were dependent on depth, and a wide range of variations was observed at shallow depths. It was confirmed that the unsaturated soil near the ground surface has the sensitive reaction induced by the infiltration and evaporation in nature.