Stress-induced AE varying characteristics in distinct lithologies subjected to uniaxial compression

Abstract

This study conducted uniaxial compression acoustic emission (AE) tests on four typical rocks with different lithologies, including coal, limestone, gypsum, and shale. In addition to measuring their stress-induced deformation process and associated AE time-varying response, this work emphatically discussed the differences in mechanical properties, fracture modes, spatial-temporal evolution, frequency band energy distribution, and nonlinear characteristics of stress-induced AE signals. According to the results, the AE energy released during the loading process and the total energy at the peak stress are closely related to the rock strength. The main microcracking fractures of coal and limestone are mixed mode with both shear and tensile components, while those of gypsum and shale are mainly tensile axial-splitting failures. The AE locations of those four tested rocks correspond to their macroscopic rupturing morphology respecitively, but with different occurrence times and spatial distributions. Additionally, the stress-induced AE events of coal, gypsum, and shale are relatively less during the pre-peak loading stages, while that of limestone begins to become frequent and reach its maximum in the crack extension damage stage. The AE frequency band energy distribution, calculated by wavelet packet decomposition, of limestone is smaller than coal, gypsum, and shale, suggesting that limestone has a larger microfracture scale than the other three rocks. However, it should be noted that approximately 90% of the energy band distribution of these four lithologies is less than 150 kHz. Besides, the nonlinear Hurst index of AE signals is greater than 0.5 when the specimens are loaded around 99% pre-peak stress. This suggests a long-term correlation between acoustic response and the loading process, with a more pronounced increase in the AE signal during the stage close to the catastrophic failure stage. The above findings provide valuable insights into the failure mechanisms of different rocks, contributing to the theoretical framework for preventing and controlling rock engineering disasters.