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Based on field geological survey and unmanned aerial vehicle (UAV) photography, this paper studied the inherent causes, intrinsic mechanisms, and kinematic characteristics of a catastrophic landslide of dissolved and fractured rock slope in a mountainous area of Southwestern China. The discrete element method (DEM) model of representative volume element of fractured rock mass considering karst existence was developed with its micromechanical parameters calibrated from laboratory element tests. The coupled finite difference and discrete element methods (FDM-DEM) were then employed to simulate deformation and failure evolution and collapse development of the rock slope with both internal and externally triggering factors properly addressed. The kinematic characteristics of mobile collapse debris flow were analyzed, and the numerical simulation results were validated by laboratory physical model test. The results show that the internal causes were mainly manifested in slope structure, lithology combination, karst, and fracture development, among which the unfavorable interaction disintegrated rock masses. The primary external cause was the staged underground coal-mining operations underneath the collapsed body, which led to large cracks appearing at the back edges of the slope. The maximum velocity of mobile collapse debris was about 65 m/s with the maximum travel distance of more than 600 m. Numerical simulation results matched well with both field forensic investigation and laboratory physical model test results. The findings would help further understand the deformation and failure process of fractured rock slope subject to underground mining and provide technical reference for accurate assessment and proper mitigation of similar landslide disasters. [ABSTRACT FROM AUTHOR]

In March 15, 2019, a small-scale loess landslide occurred at Zaoling, Shanxi Province, China, destroying several buildings and killing 20 people. Based on a digital orthophoto map (DOM) and digital elevation model (DEM) derived from Dajiang Pro4 UAV aerial images, coupled with field investigations, this paper describes the geometric features of this slope failure and analyzes its possible inducing factors. Results show that this landslide has a circular chair shape with a sliding direction of 355°. The total projected area of the landslide is 11,800 m2, in which the source is 9880 m2, and the main scarp is 1995 m2. The volume of the source material and loose deposit debris are about 10 × 104 m3 and 12 × 104 m3, respectively. Our research suggests that the inducing factors of this event may include the low strength and structure of the loess under a wet condition, special landforms of the slope, and human activities such as water discharge from a nearby bath center building and coal mining. [ABSTRACT FROM AUTHOR]

On 8 May 2022 and 12 April 2020, two large rock avalanches occurred in Zhijin County, China, in the villages of Baiyan and Baiwu, respectively. These long-runout rock avalanches had the same geological, hydrological, and topographical settings and similar triggering factors but different mobility, and this inspired a research interest in the failure and runout processes of large-volume mass movements. In this study, a detailed on-site field investigation was conducted with the aid of unmanned-aerial-vehicle-based photogrammetry and satellite imaging technologies. The results suggest that the two rock avalanches were, rather than a single factor, collaboratively triggered by multiple loading effects involving long-term underground coal-mining vibration, karstification, and cumulative precipitation. The cliff failure was dominated by the strength of the rock mass and development of the joints, while the runout was controlled by the dynamic performance of the soil on the potential sliding surface rather than the rock debris itself. The liquefaction performance of the sliding surface—consisting of coarse soils on an ancient eluvial slope in the transition area—indicates that the Baiyan avalanche had significantly longer runout and higher mobility than the Baiwu case. Although the two avalanches had different mobilities, they both briefly obeyed a physics-based statistical evaluation method—the energy line. [ABSTRACT FROM AUTHOR]