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[HDS08-12] A case study on failure and runout process of rock avalanche in Zhijin-Nayong Coalfield of China
Keywords:Rock avalanche, Coalfield geohazard, Field investigation, Slope failure
Coal-mining, a necessary energy exploitation from earth to sustain human society, has unavoidable effect on the slope instability in turn. In 2022 and 2020, a sub-vertical rock cliff, in Zhijin-Nayong field in Zhijin County, southwestern China, successively failed in Baiyan and Baiwu villages and had a long-runout travel from the source areas. These long-runout rock avalanches had the same geological, hydrological and topographical settings and similar triggering factors but different mobility, which inspired a research interest in the failure and runout processes of large-volume mass movements. In this case, triggering mechanism, runout movement and final deposition characteristics of the two rock avalanches in a coalfield was expected to be revealed and discussed in this article. Overall, the major aim is to improve understanding of the long-runout movement of large-scale rock avalanches and their failure mechanisms
In this study, a detailed on-site field investigation was conducted with the aid of unmanned aerial vehicle (UAV)-based photogrammetric technology and satellite imaging technologies. The geological settings, topographical features and precipitation data as well as the coal-mining activities relating to the rock avalanches are collected and presented in this paper.
The major results include: (1) According to precipitation records, the rainfall when the major cliff collapse occurred was lower compared to the high annual precipitation of Zhijin County. Thus, no evidence supports that these rock avalanches were directly induced by rainfall. (2) According to the historical satellite images, the cliff was successively failed in recent decade with a large number of coal-mining factories surrounding the study area. In this case, although no direct evidence quantitatively supports the correlation between underground coal-mining intensity and instability of the rock cliff, this anthropogenic effect should not be ruled out.
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 2022 Baiyan avalanche had significantly longer runout and higher mobility than the 2020 Baiwu case. Although the two avalanches had different mobilities, they both briefly obeyed a physics-based statistical evaluation method – the energy line.
In this study, a detailed on-site field investigation was conducted with the aid of unmanned aerial vehicle (UAV)-based photogrammetric technology and satellite imaging technologies. The geological settings, topographical features and precipitation data as well as the coal-mining activities relating to the rock avalanches are collected and presented in this paper.
The major results include: (1) According to precipitation records, the rainfall when the major cliff collapse occurred was lower compared to the high annual precipitation of Zhijin County. Thus, no evidence supports that these rock avalanches were directly induced by rainfall. (2) According to the historical satellite images, the cliff was successively failed in recent decade with a large number of coal-mining factories surrounding the study area. In this case, although no direct evidence quantitatively supports the correlation between underground coal-mining intensity and instability of the rock cliff, this anthropogenic effect should not be ruled out.
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 2022 Baiyan avalanche had significantly longer runout and higher mobility than the 2020 Baiwu case. Although the two avalanches had different mobilities, they both briefly obeyed a physics-based statistical evaluation method – the energy line.