Effects of bedding planes on progressive failure of shales under uniaxial compression: Insights from acoustic emission characteristics

It is believed that the bedding plane is one of controlling factors in progressive failure of shales and its characterization is of great significance in the gas shale engineering. However, it is often difficult to directly capture and visualize the progressive failure process of shales in practice. Although the microseismic method is feasible and economical to overcome this problem, to date, the effect of bedding plane on progressive failure of shales is still not fully clarified by this method. Here, we use the bonded-particle model (BPM) embedded with moment tensor algorithm to explore the progressive failure process and acoustic emission (AE) characteristics of shales under uniaxial compression. The macro mechanical behaviors such as stress-strain response and failure modes of shales were well reproduced by BPM. Meanwhile, AE characteristics were systematically monitored and analyzed during the progressive failure process. Then, the failure type dependent on layer orientation was determined by the moment tensor decomposition. And bedding-orientation-controlled crack stress thresholds as well as the degree of progressive failure could be captured by the AE cumulative number and hits. It was found that b-value in post-peak stage was susceptive to layer orientation and could be used as the indicator of the fracture complexity. Also, proportion of shear AE sources have a good consistence with fracture complexity, which suggests that shear failures favor the complex fracture formation. Our study provided a new insight into effects of bedding planes on progressive failure of shales from the viewpoint of AE characteristics.