Research on acoustic emission characteristics and mechanical properties of shale under uniaxial and conventional triaxial compression

In order to analyze the acoustic emission (AE) characteristics and mechanical properties of muddy shale under different stress conditions, uniaxial and conventional triaxial compression tests and AE tests were carried out through the MTS815 electro-hydraulic servo rock mechanics test system and the PCI-II AE system. The AE characteristics and mechanical properties were analyzed when the confining pressures were 1 MPa, 5 MPa, 10 MPa, 20 MPa, 40 MPa and 50 MPa. The results show that the peak strength, peak strain, residual strength and residual strain are linearly related to the confining pressure. The elastic modulus and Poisson’s ratio increase nonlinearly with the increase of confining pressure and can be fitted by the form of a power function, which can provide a theoretical basis for the numerical simulation tests and the theoretical calculations of geotechnical theory to accurately select mechanics parameters such as elastic modulus and Poisson’s ratio. Compared with the pre-peak ring-down count rate and energy count rate, the post-peak ring-down count rate and energy count rate are relatively high. As the confining pressure increases, the release of AE energy increases, while the AE signals decreases. In the residual stage, the AE signals generated under low confining pressure are more than those under high confining pressure. During the process of unloading confining pressure, the slope of the cumulative ring-down counts curves will increase suddenly. The AE energy generated by unloading the confining pressure under high confining pressure is generally higher than that generated under low confining pressure. This phenomenon shows that rock burst is more likely to occur under high stress conditions.