| With the increase of mining depth,the stress in the coal seam increases.The frequency and damage of typical coal-rock dynamic incidences such as coal bumps and mine earthquakes,dominated by stress increase continuously.And the evolution process for dynamic incidences is unclear.Although the mechanism of coal-rock dynamic incidences cannot be fully explained by existing theories,it is considered that these dynamic incidences are closely related to dynamic mechanical behavior of coal.In this paper,the research method of combining physical experiment and theoretical analysis is adopted,and the raw coal of Zhangminggou Coal Mine with impact risk is prepared.Through theoretical analysis,the distribution characteristics of in-situ stress field in the current mining area are summarized,and the variation laws of vertical in-situ stress and horizontal principal stress with the depth are clarified.Thus,the axial and confining stress of the test are determined.In the test,the active triaxial confining pressure SHPB test system was used to carry out the triaxial dynamic mechanical test of coal under different confining stress and different in-situ stress.The dynamic mechanical behavior of coal,the failure characteristics of specimens,and the energy dissipation were analyzed and discussed.The main results as follows:The research method combining physical experiments with theoretical analysis is adopted in this paper.The distribution characteristics of the underground stress field in the mining area are summarized by theoretical analysis,and the variation laws of vertical stress and horizontal principal stress with the depth are clarified.The experimental parameters of axial stress and confining stress are determined by combining with the core bedding of coal samples.The active triaxial SHPB test system was used in the experiment.The experimental study on dynamic mechanical properties of coal under different confining stress,and the experimental study on triaxial dynamic tests of coal with different depths were carried out.The dynamic mechanical behavior of coal,failure characteristics of specimen and energy dissipation are analyzed and discussed.The main conclusions are as follows:Experimental study on dynamic mechanical properties of coal under different confining pressures reveals the effect of confining pressure on dynamic mechanical behavior of coal.Test confining stress parameters from 2 MPa to 10 MPa,2 MPa as the confining stress gradient,6 MPa as the axial stress.The results of the study show that:（1）The peak stress of coal increases linearly with confining pressure.Through the linear fitting of the peak stress and confining stress data obtained in the five groups of tests,the fitting degree is above 95.88%.（2）With the increase of confining stress,the macroscopic crushing state of coal changed from completely crushing to powdered debris,gradually changed into small fragments,and finally not fragmented when high confining stress.The compressive strength of coal increases with the confining stress,and the deformation resistance of coal is increased.These results show that the larger the horizontal principal stress in the coal seam is,the higher the dynamic load and the energy used for the complete crushing of coal is,and the more severe the damage of dynamic incidences in the high-stress area is.In addition,the crushing characteristics of coal prove that it is feasible to judge whether the specimen is completely broken by the state for peak stress rebound in the stress-strain curve during dynamic loading.The experimental study on triaxial dynamic tests of coal with different depths reveals that the dynamic mechanical behavior of coal is caused by the change of axial stress and confining stress with depth.The results of the study show that:（1）With the increase of depth,the dynamic compressive strength of coal is steadily improved under the same loading rate.Previous studies have shown that confining stress limits the deformation of coal during dynamic loading,and the compressive strength of coal was increased.The existence of axial stress accelerates the deformation of coal,which is easier to damage and break under dynamic load,and reduces its compressive strength.Therefore,The effect of confining stress is more profound than axial stress.Meanwhile,the effect of horizontal principal stress on mechanical properties of coal is profound than vertical stress with depth increasing.In the monitoring of dynamic incidents,the effect of horizontal principal stress on coal should be considered.（2）With the increase of depth,the failure strain corresponding to the peak stress gradually increases.In the test,the energy dissipation of coal was calculated,and the energy consumption and energy dissipation density of coal per unit volume were also gradually increased.In the dynamic loading process,the energy dissipation rate of coal was mostly between 0.4and 0.5.It indicates that the energy carried by the dynamic load stress wave is well absorbed by the coal and used for the deformation,damage and fracture of the specimen itself.The energy required for crushing deformation of unit coal increases with the mining depth,and the high energy needed to cause dynamic disasters.Therefore,once the dynamic disaster occurs in the location with deeper occurrence depth,the incidence is more severe.（3）The time effect of coal deformation and fracture can be ignored while the confining pressure and axial pressure change in the dynamic loading process.The duration from loading to damage is about2.5×10-4s,and the deformation of coal sample during loading is linear stable.The results of the study can provide certain theoretical and practical support for the mechanism and prevention of coal-rock dynamic incidences,and provide certain theoretical significance and practical value.Figure[44]Table[6]Reference[116]... |
