The processes and mechanisms of collapsing erosion for granite residual soil in southern China

Purpose Collapsing erosion is a severe soil erosion phenomenon, which is widely distributed in the granite residual soil area of southern China. However, the collapsing erosion mechanism of granite residual soil remains obscure. To better understand the evolutionary process and characteristics of collapsing erosion due to rainfall, laboratory-scale experiments with varying slope angles were performed. Materials and methods Experiments of rainfall-induced collapsing erosion were conducted on a flume in which the slope angle could be manipulated. Experiments with model slopes composed of granite residual soil were preformed to observe and confirm the collapsing erosion process of slopes due to rainfall. Results and discussion Based on the experiments, collapsing erosion is closely linked to the slope angle under rainfall. The modes of collapsing erosion for flat slope and gentle slope are strip collapse and ladle collapse, respectively. When collapse occurs, the moisture content of the granite residual soil is between 30 and 40% which is less than the liquid limit of the granite residual soil 39.31%, and the steep slope that forms after the collapse can reach 80 similar to 90 degrees. Conclusions The process of collapsing erosion in granite residual soil under rainfall can be grouped into four phases: (i) raindrop splashing; (ii) sheet erosion; (iii) gully erosion; (iv) collapsing. The collapsing erosion is affected by the slope angle. The contribution of collapsing erosion to soil loss is relatively high for the steep slope under rainfall, and the development of erosion increases with increasing slope angle.