Recognition of induced charge in coal failure process and its practice of underground application

To develop and improve the monitoring technology and theory of the charge induced by the failure of coal and rock,based on the uniaxial compression experiments,the laws of change and main control factors of induced charge signals in the process of coal failure are further investigated. The generation mechanism of induced charge in the process of charged coal chips ejection is proposed. The frequency characteristics and their influencing key factors of interference and effective signals of induced charge are analyzed. The qualitative relationship among the induced charge with the stress,strain energy and deformation failure is studied. The damage statistical relationship between the loaded coal and induced charge signals is established. The evolution characteristics relationship between the induced charge and coal energy is analyzed,and the quantitative relationship between the induced charge and stress of coal is proposed. The monitoring device of induced charge suitable for complex underground conditions is developed,and the monitoring practice is carried out in the Hongyang No.3 Mine of Liaoning Province and the Pingdingshan No.11 Mine of Henan Province. The correlation of induced charge on dynamic failure of coal and rock,abutment pressure and roadway deformation are analyzed. The results show that the piezoelectric effect of coal is not the main factor affecting the generation of high amplitude induced charge signals. The comprehensive effect of crack propagation,friction slip of fracture surface and charged coal chips ejection is the principal cause making the amplitude of induced charge signals high. In particular,the amplitude of the charge signals can suddenly increase when the charged coal chips are ejected into the sensor. The main frequency of interference signals of the induced charge is consistent with the harmonic frequency of the external power supply network,and the effective induced charge signals are mainly low frequency whose distribution range with different kinds of coal is different. The intensity of induced charge is not directly related to the magnitude of stress,but directly related to the degree of nonlinear change of stress,especially positively related to the amplitude of stress drop. The intensity of induced charge can directly reflect the damage degree of coal,and can also indirectly estimate the stress of coal by analyzing the external load environment and the statistical relationship between induced charge signals and coal failure. The relationship between intensity of induced charge and elastic strain energy of coal is not significant,but significantly related to dissipation and release of strain energy,that is,the more energy dissipated and released in the process of coal failure,the higher the induced charge intensity. The intensity of induced charge is higher in the area affected by the abutment pressure of face,the area of frequent occurrence of high energy microseism and the area of serious deformation failure of the roadway. It is shown that the induced charge has a good correlation with the dynamic failure of coal and rock,the advanced abutment pressure and the deformation of surrounding rock. The technology of induced charge can be used for the monitoring and early warning of underground dynamic disaster,stope pressure and the stability of surrounding rock.