Effects of shear rates on the damaging behaviors of layered rocks subjected to direct shear: Insights from acoustic emission characteristics

Abstract

It is believed that the loading rate significantly affects the damaging behaviors of layered rocks. However, previous studies have mainly focused on the inherent bedding structure rather than the loading rate, particularly in the case of shearing. In this paper, the discrete element method (DEM) was used to simulate the rate-dependent shear behaviors of layered rocks under direct shear tests. Then, the rate-dependent acoustic emission (AE) characteristics were systematically investigated based on the moment tensor theory. The results showed that the shear rate significantly affects the failure process and AE characteristics of layered rocks. With the increase in the shear rate, the average released AE energy increased, while the total AE number and b-values decreased, which indicates that the crack propagation rate and the proportion of high-energy AE events increased. As a result, a macroscopic failure occurred for the rocks at the peak strength point under low-rate shearing and at the postpeak stage under high-rate shearing. In addition, a high-energy AE event corresponded to the crack damage point defining the boundary between the stable and unstable failure stages, thus providing an efficient method for capturing the damage precursors of rock failures. Under this premise, the characteristic stress and strain thresholds were investigated to discuss the feasibility of predicting the failure of layered rocks while considering the shear rate. Overall, this study provides new insights with regard to the effects of the shear rate on the damaging behaviors of layered rocks from the viewpoint of AE characteristics.