Damage process and failure mode of stratified shale under uniaxial load
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Abstract:
Low permeability is one of the main factors restricting shale gas exploitation, and the type and complexity of fractures in rock mass are key factors affecting permeability. Therefore, strengthening the study of shale damage and failure process is of great significance for improving the efficiency of shale gas exploitation. In this study, based on a combination of experimental methods and numerical simulations, the damage evolution, crack development, fractal characteristics, and influencing factors of stratified shale under uniaxial load are deeply investigated. The results show that the development of micro-cracks follows a trend of “steady rise - basically stable - rapid rise” during the loading of specimens. In terms of the stages of micro-crack development, tensile cracks dominate at 0° and 90° bedding angles with proportions of 94.7% and 96%, respectively, while shear cracks dominate at 30° and 60° bedding angles with proportions of 65% and 86.9%, respectively. The macroscopic failure cracks exhibit obvious fractal characteristics, with fractal dimensions of 4.25, 3.44, 2.06 and 3.60 at bedding angles of 0°, 30°, 60° and 90°, indicating that complex cracks are more likely to form when the load is perpendicular to the bedding direction. The law of damage development is affected by bedding orientation. Damage is concentrated in the matrix at 0° and 90° bedding angles and in the bedding at 30° and 60° bedding angles. In addition, damage is affected by the heterogeneity and anisotropy of the rock. For example, with an increase in the variance of the elastic modulus, the homogeneity of the specimen decreases, and the damage range under the same load increases. Conversely, with an increase in bedding stiffness, the anisotropy of the specimen decreases, and the damage range under the same load increases.
