Failure Mechanism Of Mining Induced Tremor And Response Law Of Its Source Mechanics Parameters

As the depth and intensity of coal mining in China increase on a daily basis,the results of rock burst are becoming increasingly severe.Mining tremor is the indispensable part that gestates and triggers rock burst.Therefore,the study on the failure mechanism of mining tremor is essential to perfection of the disaster-causing mechanism of rock burst.In this paper,the relative moment tensor inversion method was proposed as the inversion method of mining induced tremors' failure mechanism.The construction of moment tensor inversion matrix was optimized based on microseismic observation conditions.A method for identifying the failure mechanism suitably for mining induced tremors was proposed.The characteristics and correlation of key source mechanical parameters were analyzed.The failure mechanism of burst sources and the response law of source mechanical parameters under different characteristics are studied.The main conclusions are as follows:The analysis result of the inversion feasibility of moment tensor suggests that relative moment tensor inversion is suitable to the geological and monitoring conditions of coal mines in China nowadays.Based on its fundamental ideas,the inversion matrix construction has been optimized in combination of the actual situations of onsite monitoring,and the number conditions of sources,rays and far field displacement required by relative moment tensor inversion,and the development of Matlab program of mining induced tremors failure mechanism has been completed.The mining tremor belongs to general dislocation point model,and particle swarm optimization is believed to be more accurate,effective,and more direct for the solution of moment tensor parameters.Based on the basic types of mining tremor,their moment tensors are decomposed into ISOM +DCM +CLVDM.Dislocation angle is used to determine and identify the fundamental parameters of mining tremor failure mechanism.The compressive,shear and tensile strength ratios of coal and rock mass are used as the basis for different failure types.The particle swarm optimization was used to optimize the source mechanical parameters solution based on Brune model,and the burst sources inside the sources database are used as the research subjects,and the key source mechanical parameter characteristics of burst sources are studied.The results showed that there is a positive logarithmic correlation between the seismic moment and the radiant energy.Apparent volume is able to characterize the differences among various scales of mining tremor failure,while the source radius is inclined to characterize the macroscopic scale of coal-rock mass failure.Stress drop is more inclined to characterize the overall failure effects of quake sources,while apparent stress is inclined to characterize the failure efficiency of quake sources.The results of the study on the correlations of various types of source mechanical parameters show that there is a significant positive correlation between the seismic moment of burst sources and apparent volume and stress drop.Unreasonable seismic moments,apparent volume and stress drop parameter ratios are all able to decrease the hazard degree of mining tremor.There is a positive logarithmic relationship between apparent volume and stress drop,and the overall levels of both is positively correlated with the onsite severity.Apparent stress is positively correlated with onsite severity,and can be singled out to be used as the indicators of the assessment of source intensity or burst hazard degree.The mining tremor hazard index T is proposed,based on the correlations of quake source mechanical parameters,which is used to characterize the burst hazard level.The study results show that the result based on T values is the modification and optimization of radiation-based energy assessment results,which is helpful to improve the monitoring and early warning efficiency of rock burst.The failure mechanism of burst sources are mostly tensile events under the folded structure conditions,of which the failure forms are mostly the collapse of coal and roof caving or separation.The failure mechanism of burst sources and strong hazardous mining tremors are mostly shear events under the deep fault structure conditions,of which the failure forms are mostly the shear landslide of fault structure and the shear destruction of coal and rock mass under pressure.The failure mechanism of burst sources and strong hazardous mining tremors of in-depth burial main roadway coal pillar area are mostly shear events,the majority of shear failures are originated from the coal pillar shear destruction under high stress state.The source mechanical parameters of mining tremors under different characteristic conditions and failure mechanism have little differences.Nevertheless,mining tremors of dominating failure types tend to have relatively strongger apparent volume,indicating that more coal and rock masses are involved in the failure process as the media.The method of calculating the failure mechanism and the mechanical parameters of the mining induced tremor proposed in this paper can further excavate the information of rock burst,and provide scientific basis for guiding early warning and danger relief of rock burst on site.