Study on macroscopic and microscopic damage and evolution of coal rock based on acoustic emission time-varying characteristics

To study the acoustic emission (AE) time-varying and frequency spectrum characteristics of coal and rock deformation and failure in deep mines under high temperature and high stress, and then reveal the acoustic precursor characteristics of coal and rock deformation and fracture. In this paper, the time series of AE signals under different thermal-mechanical conditions are tested and analyzed by four experimental unconstrained heating, uniaxial compression, graded loading, and temperature-pressure coupling. It is found that the AE signals increase gradually with the increase of temperature and load. Based on this, the AE frequency domain characteristics of coal rock fracture process under staged loading and thermal-pressure coupling conditions were analyzed. The results showed that the AE signals coexisted in the high and low frequency bands, the amplitude of the high-frequency signals changed slightly, and the low-frequency high-amplitude phenomenon appeared. Finally, the time-frequency acoustic signal characteristics are tested before and after the rock burst in the coal mine site. The laws of space-time evolution of microearthquake energy and frequency before and after rock burst are studied. It is found that the phenomenon of “lack of earthquake” begins to appear three days before the rock burst. The amplitude of the signal increased at the pre-seismic time, and the low-frequency signal developed. Based on this, the precursor characteristics of unstable fracture of impact ground pressure were discussed. The research of this paper will provide theoretical support and practical basis for the monitoring and early warning of coal and rock dynamic disasters.