Study on the Failure Mechanism and Permeability Characteristics of Gas Containing Sandstone Intercalated Coal

[Image: see text] The deformation failure mechanism and permeability characteristics of loaded coal sandstone samples under triaxial stress loading were analyzed based on the experimental platform of the coal-rock fluid solid coupling triaxial servo system. The results show that the stress–strain curve of coal intercalated sandstone can be divided into five stages: compaction closure, elastic deformation, stable fracture expansion, unstable fracture expansion, and post-peak strain softening. With the increase of confining pressure, the peak strength and residual strength of the sample increase linearly with the confining pressure. The permeability of the sample decreases slowly with the increase of axial strain, increases rapidly after reaching the stage of unstable fracture propagation, and changes in “V” shape. The relationship between initial permeability and confining pressure can be fitted with exponential function. Based on the fracture volumetric strain model, the progressive failure mechanism of damage expansion of coal mixed sandstone is discussed. The fracture volume strain of each sample under different stress states is given, and the failure mode and crack distribution characteristics of the sample are obtained. The research results can provide reference for reasonable, safe, and efficient coal mining and gas disaster control.