| During the transition from open-pit to underground mining,various factors such as rainwater infiltration and mining-induced unloading affect the dynamic changes and interactions of stress fields,leading to the development,connectivity,and collapse of overlying rock fractures.Understanding the failure mechanism and evolution process of this phenomenon is crucial for underground mining engineering.In this study,a physical model experiment was designed based on the actual geological conditions of the Huangniu Front Slope in Dexing Copper Mine to analyze the failure process of rock masses at different slope angles under the coupling effect of rainfall and mining.The deformation and failure modes were systematically studied,and the evolutionary characteristics of the crack network were analyzed using chaos theory.A regression equation was derived for the fractal characteristics of the crack network with respect to slope angle,and percolation theory was introduced to explore the evolution law of the crack network.This research sheds light on the rock failure mechanism and crack network evolution characteristics of different slope angles under the coupling effect of rainfall and mining.(1)A comprehensive study was carried out on the engineering geological,geological,hydrological conditions,and slope failure modes of the Huangniu Front Slope in Dexing Copper Mine.Relevant data was recorded,and rock samples were collected for physical and mechanical testing.Using similarity theory calculations based on actual parameters,various data of the physical model were determined,which can serve as a reference for establishing numerical simulation models.(2)Indoor experiments were conducted using a rainfall simulation test bench to investigate underground mining under the coupling effect of rainfall and mining for different slope angles.The analysis of water content,pore water pressure,and displacement revealed that both pore water pressure and water content increased continuously with rainfall.Water content was inversely proportional to depth,while pore water pressure was directly proportional to depth.Higher levels were observed at the open-pit platform due to the impact of rainfall and accumulated water under the slope.The rock mass moved slightly towards the mining area during the openpit mining stage.Vertical cracks appeared in the overlying rock during mining,and the cracks above the mining room continued to develop and connect,resulting in a semi-elliptical combination.After pillar mining,significant displacement occurred in the overlying rock area,disjunctive fractures appeared,and large-scale collapse of the overlying rock occurred after continuous pillar mining.(3)Numerical simulations were conducted using discrete element software to investigate the slope failure under the coupling effect of rainfall and mining for different slope angles.The results were consistent with those from physical model experiments.The stress distribution,failure patterns,and energy conversion of models with different slope angles were simulated,and the mechanisms of each stage were analyzed in combination with the results of indoor physical experiments.The findings indicated that during the open-pit mining stage,greater slope angles resulted in more severe damage.The reduction of elastic potential energy during the mining room stage was similar to the decrease of mechanical energy.During the pillar mining stage,stress was concentrated at each goaf,and the proportion of mechanical energy reduction exceeded that of elastic potential energy reduction.After continuous pillar mining,stress was concentrated in the failure area,and the slope angle effect on mechanical energy reduction became increasingly significant after the model collapsed completely.(4)Mining-induced overlying rock fracture networks exhibit fractal characteristics and can be described using the fractal dimension.The fracture network was divided into grids of varying sizes,and the fractal dimension of the fracture network for different slope angle models was determined by calculating the slope of each grid.Through comparison of the fractal dimensions of the fracture networks generated by different slope angle models,it was observed that the fractal dimension initially decreased and then increased as the slope angle increased from 45° to 65°.A regression equation for the fractal dimension as a function of slope angle was calculated.(5)The overlying rock fracture network can be classified into collapse,interconnect,and extension zones based on the distinct characteristics of different fractures.The fractal dimensions of these three zones were analyzed,and it was found that the relationship between the fractal dimension and slope angle differed for each zone.Regression equations were calculated for the fractal dimensions of these three zones as a function of slope angle.Furthermore,percolation theory was applied to investigate the evolution law of the fracture network.The percolation rate was calculated for the fracture network under different slope angles,and it was used to describe the expansion speed and connectivity failure of the fracture network. |
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