Under rapid global climate change, the risk of ancient landslide reactivation induced by rainfall infiltration is increasing significantly. The contribution of cracks to the reactivation of ancient landslides, as an evolutionary product, is a topic that deserves attention; however, current research on this issue remains insufficient. In this study, taking the Woda landslide in the upper Jinsha River as a case study, we investigated the reactivation mechanisms of ancient landslides with and without cracks under rainfall based on model tests. The study showed that cracks influence the reactivation range and depth of ancient landslide. In cases where no cracks develop on ancient landslides, rainfall can only cause shallow sliding with failure concentrated at its front edge. Conversely, when cracks develop on ancient landslides, rainwater can quickly infiltrate into the sliding zone along the cracks and induce overall reactivation of the ancient landslide. Furthermore, the reactivation mechanism of ancient landslides without cracks is that the failure of ancient landslide foot results in progressive failure at the front of the ancient landslide. When cracks have developed at ancient landslides, the reactivation mechanism of which involves mid-rear ancient landslide creeping, tensile cracks develop on the mid-rear ancient landslide, with localized sliding at the front edge, tensile cracks extending, local sliding range extending, accelerated creeping, and progressive failure of the mid-rear ancient landslide. These findings shed light on how cracks influence rainfall-induced mechanisms of ancient landslide reactivation and hold great significance for advancing our understanding regarding these mechanisms.

The southwestern mountainous region of China is tectonically active and characterized by high, steep anti-dip rock slopes with weak intercalations. Under seismic action, the dynamic response characteristics of these slopes are complex, and the mechanisms of deformation and damage remain unclear, hindering effective disaster risk prevention and control. Based on extensive investigations of high and steep slopes in the upper reaches of the Jinsha River, a conceptual geological model is developed. It examines the dynamic response characteristics and deformation failure of the slopes under varying conditions of peak ground acceleration(PGA), seismic wave frequency, and loading direction through large-scale shaking table model tests. The results indicate pronounced nonlinear dynamic response characteristics of weak interlayer anti-dip rock slopes under seismic action, exhibiting significant height and surface effects. As the PGA increases, these two dynamic amplification effects become more prominent. The vertical dynamic response of slopes within the range of 1/3h to 2/3h demonstrates a surface effect when subjected to sinusoidal waves. As the frequency of sinusoidal waves increases, the region exhibiting a greater dynamic response gradually shifts from 1/3h to 2/3h towards the foot of the slope. When PGA≥0.4 g, under the action of a 2 Hz sinusoidal wave, the dynamic response in the damage area at the top of the slope shows signs of decay. Under the influence of the Wenchuan wave, the horizontal dynamic response at the slope's top and surface is significantly weaker than the vertical dynamic response. However, under the effect of high peak ground acceleration(PGA≥0.4 g) seismic waves, an opposing pattern is observed. The vertical dynamic response in the upper range of 1/2h to 5/6h of the slope is stronger when loading occurs simultaneously in the x and z directions compared to loading the Wenchuan wave solely in the x direction. The deformation and failure process of the slope model can be categorized into five stages: the tiny damage stage, the cracking stage at the slope top, the failure stage at the slope shoulder, the evolution stage of the sliding surface, and the instability stage of the sliding surface.

Claystone is actually a type of hard soil or soft rock. To reveal the engineering geological characteristics of the Xigeda formation claystone in Luding County (Western Sichuan, China), some experiments, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and geotechnical tests, are performed. The testing results indicate that the Xigeda formation claystone primarily consists of silt, clay, and other fine-grained materials. It is characterized by interbedded yellow and gray thin layers with a horizontal lamination structure. The yellow and gray claystones are made of the same materials but differ in their proportions. Additionally, yellow claystone is characterized by a higher density, resulting in enhanced cementation among clay particles. The permeability coefficient of Xigeda formation claystones ranges from 3.62 × 10⁻⁴~7.34 × 10⁻⁴ cm/s. The cohesion of yellow and gray claystones decreases with increasing moisture content, and the decline is greater at higher moisture contents. However, the relationship between internal friction angle and moisture content is different. The mechanical properties of the Xigeda formation exhibit significant differences in sensitivity to changes in moisture content across various regions. Notably, the claystone within the study region experiences a particularly pronounced weakening of its mechanical properties when exposed to water.