Mechanical Response and Acoustic Emission Characteristics of Laminated Gulong Shale under Cyclic Loading

ABSTRACT In the context of escalating global energy demands, shale oil, a pivotal unconventional hydrocarbon resource, has garnered considerable attention because of its substantial reserves and considerable development potential. Cyclic loading tests are utilized to simulate the complex mechanical behavior of shale under repeated cyclic stress during actual exploitation. These tests unveil the deformation and failure mechanisms of shale and provide theoretical guidance for safe and efficient extraction. This study investigates the mechanical properties and acoustic emission (AE) characteristics of shale with varying bedding angles (0°, 30°, 45°, 60°, and 90°) under uniaxial cyclic loading and unloading conditions. Utilizing the findings from these experiments, a cumulative damage model is formulated under varying initial stress levels. The outcomes demonstrate that, as the initial stress ascends from 50 % to 80 %, the stress–strain curves of shale manifest conspicuous nonlinear characteristics, accompanied by an augmentation in hysteresis loops and substantial strain accumulation. The compressive strength of shale displays a regular trend of first decreasing and then increasing with bedding angle, with the weakest region at 45°, where compressive strength reaches its minimum. The elastic modulus displays higher values at low bedding angles (0° and 30°) and significant decreases at high bedding angles (60° and 90°), with the unloading phase demonstrating a more pronounced reduction in elastic modulus. AE analysis reveals that crack activity is most intense at a bedding angle of 60°, predominantly governed by shear failure, whereas tensile failure is the primary mode for bedding angles of 0° and 90°. A novel cumulative damage model is established based on the number of AE events, which quantitatively characterizes the damage evolution and demonstrates high accuracy upon validation. The bedding angle exerts a substantial influence on the damage accumulation rate and the crack propagation mode, although the initial stress level determines the intensity and extent of crack propagation. These findings offer critical insights into the mechanisms and dynamics of crack propagation in these materials.