Study On The Law Of Electric Charge Induction In Gassy Coal-rock Failure Process And Its Application

It is a mechanical process of energy accumulation and release in coal-rock where electric charge signal occurs accompany with the deformation and failure process,which can reflect the internal condition of coal-rock indirectly and also has a great significance for monitoring coal-rock deformation and failure.Electric charge monitoring of coal-rock has been applied to the monitoring and early warning of rockburst in coal mines,as well as some achievements have also been gained.However,many problems and difficulties still exist in the investigation of the electric charge initiation mechanism in failure process of gassy coal-rock and application of gas dynamic disaster monitoring.Systematic investigation on the law and application of coal-rock containing gas failure with electric charge induction has been carried out based on theoretical analysis combining with experimental study,as well as the electric charge monitoring equipment developed and calibrated independently for gassy coal-rock.Based on the interface barrier formation mechanism of coal-rock micro-crack,three free charge formation mechanisms of gassy coal-rock,micro-crack slippage and separation,particle friction and collision and gas migration and carrying particles in pores are proposed,which provide a theoretical basis for the study on the law of coal-rock failure with electric charge induction.In view of the bad environment in coal mine,a non-contact charge sensor based on the inductive principle is manufactured,portable coal-rock charge monitor based on MSP430F449 SCM and an online charge monitoring system is further developed.Moreover,in order to study the quantity of electric charge quantitative in the process of coal-rock failure,the calibration test system of coal-rock charge sensor is designed.The modified charge-voltage conversion coefficient of coal-rock charge sensor is 80mV/pC by the calibration test.By using the conversion coefficient,the sensitivity coefficient K of the sensor under different frequency response is close to 1,which indicates that the calibration effect is fairly well.With the designed triaxial compression charge monitoring test device of gassy coal-rock and the charge monitoring test device for gas migration in coal-rock,tests of the charge induction law of coal-rock failure are performed under the influence of loading mode,gas and bursting liability.Test result shows that charge signal in coal-rock is the instantaneous pulse cluster signal and the stress,gas and bursting liability have significant influence on it.Confining pressure can amplify and strengthen the electric charge signal.Nevertheless,on the one hand,the gas can reduce the charge signal by weakening the strength and bursting liability of coal-rock.On the other hand,the internal cracks coalesce near the limit strength of coal-rock and gas can form into steaming current to enhance the charge signal through its own rapid flow characteristics.Besides,different forms of stresses cause the propagation of micro-cracks and make the damage more localized in coal-rock and which is the important reason for the free charge generation.Based on the unified theory of rockburst and outburst,the mechanism of compound dynamic disaster of rockburst and coal and gas outburst is revealed and based on the theory of disturbance response instability,the critical formula of compound dynamic disaster in the circular tunnel of gas coal seam is deduced.Rock mass stress,gas pressure and coal-rock bursting liability are the main controlling factor of the compound dynamic disaster.Moreover,a new idea of applying the electric charge induction method to coal mine compound dynamic disaster monitoring and early warning is proposed based on the sensitive of charge signal toward to stress,gas and bursting liability.To this end,the 8th coal mine in Pingdingshan and Jixian coal mine in Shuangyashan are choosed to carry out the field application of the charge monitoring equipment.The results of field application indicate that in the mining of surfaces of stable deposit and no geological structures,the most value,mean value and variation coefficient of coal-rock can reflect the type of disaster and the degree of danger in the initiation of dynamic disaster and the electric charge signal is associated with the change of stress and gas.The field application of charge monitoring equipment indicates a strong anti-jamming capability,achieving the automatic monitoring and network management on coal mine dynamic disaster preliminary.