Experimental study on the microseismic, sound, and acoustic emission characteristics of different damages in granites subjected to various loads

The mechanical properties of rocks with different degrees of damage can affect the safety and stability of underground engineering projects, and their acoustic characteristics relevant to the analysis, prediction and early warnings of internal failure. In this study, uniaxial compression, biaxial compression, direct shear and Brazilian splitting tests of granite were performed, and the entire process of rock failure was monitored in real time by microseismic (MS), sound, and acoustic emission (AE) systems. The variations in granite strength and deformation characteristics under different stress states versus the initial damages in rock were studied, and the evolution characteristics of MS, sound, and AE signals of granite with different degrees of damage under various stress states were compared and analyzed. The results show that: (1) Under various stress states, granite strength significantly decreases with increasing initial damage, and the corresponding magnitude of each decrease in strength follows the order of Brazilian splitting strength > uniaxial compressive strength > shear strength > biaxial compressive strength. Moreover, as the initial damage increases, the failure characteristics tend to transform from brittle failure to ductile failure, and the compressive failure mode changes from tension-based failure to shear-based failure. (2) The evolution of the MS, sound, and AE signals of rock specimens with different degrees of damage generally exhibits significant differences when D > 0.37 and D < 0.37. (3) Based on the evolutionary characteristics of MS, sound and AE signals, precursor information about rock failure and the initial damage in rock can be obtained. In general, for rocks with different degrees of damage, MS signals provide the most abundant precursor information and criteria, followed by AE signals and sound signals. These differences are related to the differences in the signal frequency band, acquisition frequency, acquisition mode, and sensitivity of the three types of acoustic signals.