Acoustic Emission Characteristics During the Microcracking Processes of Granite, Marble and Sandstone Under Mode I Loading

We conduct a comparative laboratory investigation of the cracking behaviour of granite, marble and sandstone using semi-circular bending (SCB) tests on pre-notched specimens with acoustic emission (AE) monitored. We analyze and compare the spatial–temporal evolution, relative amplitude, and source mechanisms of the AE events. To explain the differences in the AE characteristics, we examine the microscopic features of macrocracks induced in the SCB tests using the thin-section petrographic analysis. We find that the temporal evolution patterns of AE events are generally similar among the three rocks. Most AE events are observed in the granite and the least in the sandstone. The AEs in the granite and marble both concentrate near the notch tip, while those in the sandstone distribute along the macrocrack path. The AEs in the granite and marble may be mainly attributed to the reactivation of pre-existing microcracks near the notch tip. The AEs in the sandstone could be more induced by the nucleation of new microcracks in the area where the macrocrack would subsequently form. For all three rocks, the tensile events are the predominant event type. Much more shear events are observed in the granite as compared with the marble and sandstone. These differences in the quantity, distribution and source mechanisms of AE events are related to the distinct microstructural characteristics of the three rocks. Our results provide valuable insights into the understanding of the correlation between rock microscopic features and characteristics of AE activities that may facilitate more rigorous AE analysis in rock engineering practice.