Study on the multiparameter evolution law and precursors of microearthquakes during the collapse process of slopes with structural surfaces

Under the influence of mining, the rock mass of a slope with a structural plane gradually deteriorates and is prone to collapse, which poses a threat to the safety of personnel and equipment. In this work, the spatial and temporal evolution of multiple microseismic parameters during the collapse of a slope with a structural surface is studied via field monitoring and numerical simulation, and the mining activities and the collapse precursor of the slope are analyzed. The results show that the daily microseismic event rate presents an unusually rapid increase before the slope collapses. The increase in the microseismic event rate 5 days before the collapse is 40 % greater than that 5 to 15 days before the collapse. The cumulative apparent volume increased 2 to 3 days before the collapse, whereas the energy index decreased. An aggregation index of microseismic events is proposed to characterize the density of microseismic events in a slope. The clustering index decreases significantly 2 to 3 days before collapse, and the minimum values are all less than 0.2, indicating that the density of microseismic events in the collapse area increases significantly before collapse. The time when the energy released by a microseismic day is greater than 10⁶ J accounts for 70.8 % of the total time and shows a sudden decreasing trend before the collapse. The numerical simulation revealed that the increase in displacement, stress, and shear strain in the study area suddenly increased 2 to 3 days before the collapse, and the slope rock mass in this area was in an unstable state. Therefore, 2 to 3 days before collapse, the daily microseismic event rate increased while the daily energy decreased, the cumulative apparent volume increased while the energy index suddenly decreased, and the aggregation index rapidly decreased. These three phenomena can be used as precursors of slope collapse. The research results can provide theoretical support for slope stability research and warning of collapse under similar conditions.