Energy-based evaluation of sandstone brittleness under triaxial compression: Micromechanical damage approach

Rock brittleness is a critical property in geotechnical and energy engineering, as it directly influences the prediction of rock failure and stability assessment. Although numerous methods have been developed to evaluate brittleness, many fail to comprehensively account for the impacts of microstructural changes, mineralogical characteristics, and stress conditions on energy evolution during failure. This study proposes a novel approach for brittleness evaluation based on the energy evolution throughout the post-peak failure process, integrating two micromechanical mechanisms: crack propagation and frictional sliding. A new brittleness index is defined as the ratio of generated surface energy to released elastic energy, providing a unified framework for assessing both Class I and Class II mechanical behaviors. The brittleness of cyan, white, and gray sandstones was investigated under various confining pressures and moisture conditions using X-ray diffraction (XRD), scanning electron microscopy (SEM), and conventional triaxial compression (CTC) tests. The results demonstrate that brittleness decreases with increasing confining pressure, due to suppressed crack propagation, and increases under saturated conditions, as moisture enhances crack propagation. By establishing connections between mineral composition, microstructural features, and stress-induced responses, the proposed method overcame limitations of previous approaches and offered a more precise tool for evaluating rock brittleness under diverse environmental scenarios.