Response of granitic residual soil slopes to alternating loading of multiple types

Granitic residual soil slopes are widely distributed in coastal areas of southern China. The alternating wet-dry conditions caused by rainfall and drying readily trigger their instability. However,the properties of granitic residual soils often vary significantly across different regions,leading to diverse response characteristics. This study investigates the slope surface erosion and desiccation cracking behavior of a granitic residual soil slope in Qingyuan,Guangdong Province,under alternating wet-dry conditions through laboratory-scale model tests. Furthermore,numerical simulation methods were employed to refine the understanding of the failure evolution mechanism of the slope under rainfall. The results indicate that regarding the failure mechanism,the high water absorbency of the granitic residual soil slope and the consequent loss or decrease in matrix suction are key factors leading to landslides. However,the loss of matrix suction tends to be a sufficient rather than a necessary condition for slope instability. In terms of failure mode,when the rainfall intensity is greater than 2.4 mm/h,slopes with a higher coarse-grained content are prone to surface erosion failure without a distinct slip surface. The drying process significantly influences the slope stability during subsequent rainfall events. This is manifested in the network of desiccation cracks(approximately 1 mm wide and 10-30 mm deep) formed on the slope surface due to drying,which create preferential pathways for rainwater infiltration,thereby exacerbating the erosion of the surface residual soil. The findings of this study may provide a theoretical basis for hazard assessment and mitigation of granitic residual soil slopes under alternating rainfall-drying conditions.