Experimental study on physical simulation of reactivation mechanism of ancient landslides under rainfall condition

Water is a crucial factor leading to the reactivation of ancient landslides. However, soil‒rock mixed landslides that have undergone long-term consolidation typically exhibit low permeability. The mechanism by which surface water generated by rainfall infiltrates and triggers landslide reactivation remains unclear. Based on the investigation of reactivation cases, this study explores the reactivation mechanism under the coupling effect of rainfall and cracks using landslide physical model tests. The results show the following: (1) Cracks can affect the seepage rate and depth of the landslide body. Without surface cracks, the landslide body has a low permeability coefficient, and rainfall can only cause shallow landslide. When surface cracks develop, rainwater can quickly infiltrate along the cracks to the deep sliding zone, triggering the reactivation of ancient landslides. (2) The location of the cracks can affect the reactivation mode of ancient landslides. Without cracks, ancient landslides exhibit a gradual retrogressive erosion reactivation. With cracks, reactivation deformation initially appears as retrogressive erosion, and gradually expanding to sliding along the preset cracks at the front edge, followed by tensile deformation and forward pushing at the rear edge, ultimately leading to overall reactivation sliding due to the combined effects of front traction and rear pushing. (3) Before sliding, both deep pore water pressure and soil pressure rapidly increased and then quickly release after sliding. Therefore, abrupt change in pore water pressure and soil pressure can be taken as the critical criterion for the reactivation of ancient landslides.