Effect of rainfall intensity on failure mode of granite residual soil slope under dry-wet cycle

Granite residual soil is widely distributed in the southeast of China, where slopes composed of this material are prone to instability and failure under alternating rainfall and drying conditions. To investigate the effect of rainfall intensity on the damage pattern and characteristics of granite residual soil slopes under the wet-dry cycle, this study employed scaled-down physical model tests simulating three cycles of wetting and drying under two distinct rainfall intensities. The experiments examined slope deformation, volumetric water content, and changes in matric suction. The results show that when the rainfall intensity is 0.7 mm/min, the matric suction tends to zero after 15 min, and the slope is mainly shallow sliding failure with obvious sliding surface. When the rainfall intensity is 1.6mm /min, the rainwater forms slope runoff, the matric suction tends to zero after 15 min, and the slope is mainly damaged by surface erosion without obvious sliding surface. Different rainfall intensity changes the failure mode of the granite residual soil slope, and the dry-wet cycle accelerates the instability failure of the granite residual soil slope. This acceleration is mainly reflected in the dominant seepage channels of rainwater caused by the drying effect, which in turn leads to the loss of the soil matrix suction. This study can provide basic information for the development of targeted protective measures for granite residual soil slopes under different rainfall intensities.