Moisture content, pore-water pressure and wetting front in granite residual soil during collapsing erosion with varying slope angle

Collapsing erosion is very severe in subtropical regions that are covered extensively by granite residual soil. However, detailed information about hydraulic responses during collapsing erosion, especially for different slope angles, remains unclear. Therefore, to control collapsing erosion, it is important to attain a more comprehensive understanding of the complex hydraulic responses due to rainfall. In this study, an artificial rainfall simulator and an experimental device were used to evaluate the collapsing erosion process, with particular consideration of the influence of slope angle. Flume experiments using three slope angles (0, 10, and 20°) were performed under artificial rainfall. This study explored the evolutions and hydraulic responses of collapsing erosion of granite residual soil by simultaneously monitoring moisture content, pore-water pressure, and wetting front during heavy rainfall. The results showed that collapsing erosion occurred faster with steeper slope angle. Collapse occurred in an upslope direction, when the corresponding moisture content of the soil was between 30% and 40%. Pore-water pressure increased until the development of collapsing erosion but was released when the soil mass collapsed. The descending process of the wetting front on a gentle slope and a steep slope can be divided into two stages and three stages, respectively. This study presents an improved characterization of collapsing erosion and provides valuable evidence for slope-angle impacts on infiltration events during collapsing erosion under heavy rainfall.