Acoustic emission response characteristics of loaded tectonic coal failure process under low pressure environment

The uniaxial compression experiment under low pressure environment was carried out by using tectonic coal samples. The acoustic emission response characteristics of coal fracture in low pressure environment were obtained by using fast Fourier transform (FFT) and wavelet packet decomposition. The results show that when the loading stress of coal increases, the acoustic emission spectrum becomes more abundant, and the overall trend shows a left shift. When the gas pressure increases, the frequency spectrum of the acoustic emission signal gradually transitions from the initial low-frequency high-energy state to the high-frequency low-energy state, and its frequency range gradually narrows. At the same time, the original complex multi-peak shape is gradually simplified into a single peak shape. As the stress increases, the proportion of acoustic emission energy in the frequency band of 0-4.38 kHz gradually increases, while the acoustic emission energy in other frequency bands gradually decreases. The signal energy proportion in the two frequency bands of 2.92-4.38 kHz and 4.38-5.84 kHz has the most obvious response trend to stress change. When the air pressure changes, the proportion of acoustic emission energy in the three frequency bands of 2.92-4.38 kHz, 4.38-5.84 kHz and 7.30-8.76 kHz shows a significant response trend with the change of air pressure. This phenomenon shows that the two frequency bands of 2.92-4.38 kHz and 4.38-5.84 kHz are the characteristic frequency bands of tectonic coal fracture process.