Two long-runout rock avalanches in 2022 and 2020 in an underground coal mining field in Zhijin, China

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.

Automated summary

Two large rock avalanches occurred in Zhijin County, China, in Baiyan and Baiwu villages on 8 May 2022 and 12 April 2020, respectively. Despite having similar geological, hydrological, and topographical settings as well as triggering factors, the two avalanches had different mobility. A detailed on-site investigation using unmanned-aerial-vehicle-based photogrammetry and satellite imaging technologies revealed that the avalanches were collaboratively triggered by multiple loading effects such as underground coal-mining vibration, karstification, and cumulative precipitation. The cliff failure was influenced by the strength of the rock mass and joint development, while the runout was controlled by the dynamic performance of the soil on the potential sliding surface. The Baiyan avalanche had significantly longer runout and higher mobility compared to the Baiwu case due to the liquefaction performance of the sliding surface consisting of coarse soils in the transition area. Both avalanches briefly followed a physics-based statistical evaluation method called the energy line.