Failure process and modes of rockfall induced by underground mining: A case study of Kaiyang Phosphorite Mine rockfalls

The analysis of the failure processes and mechanisms of rockfalls that are associated with underground mining activities is presented. The study area is located in Kaiyang Phosphorite Mine in Southwest China, where the geological condition is dominated by anti-dip slopes with layers inclined backward into the natural slope with decreasing strength in the rock mass from the upper (dolomite-rich) to the lower (shale-rich) strata. The analysis is based on field investigation and laboratory experimental study using a gravitational simulation device. The results support the proposed failure mechanism by demonstrating the process of failure from the deformation of the roof and floor in the stopes, to the development of surface cracks near the top of slopes, and eventually to the formation of rockfalls as the surface cracks propagate along pre-existing joints. The rockfalls are classified into one of three failure modes: crack-toppling, crack-sliding, and crack-slumping, in which the failures are governed by the corresponding characteristics of the rock mass structure. The study of the failure process and their spatial and temporal correlation with the underground workings reveals warning signs or indicators of impending slope instability. Improved understanding of the failure process and indicators can aid in early identification and timely warning of geohazards in phosphorite mines.