Influence of Stress and Crack Patterns on the Sensitive Characteristics of Fissure Sandstone Permeability under Hydromechanical Coupling

The stress-sensitive of seepage characteristics after rock fracture has a crucial effect on the formation and closure of seepage channels, and it is important to study the sensitivity of fracture permeability for engineering seepage prevention. The aim of the current study was to investigate the permeability law of different fracture modes under unloading action. Firstly, the physical and mechanical parameters of the Voronoi polygon block and joint were fitted with rock properties obtained in the laboratory based on the fracture characteristics of triaxial seepage experiment samples. Crack reconstruction technology and a new hydraulic parameter fitting method were used to obtain the hydraulic aperture of microjoints and macrocracks. Then, six single crack models and four models based on typical fracture characteristics of rock samples were established to study the variation of the hydraulic aperture of microcracks and macroscopic cracks in unloading environment and the morphology of the main seepage passages, to explore the seepage characteristics of different angle cracks under different unloading stress paths, and to analyze the law of seepage variation of different crack forms under different stress environments. The results indicated that a horizontal hydraulic aperture is more sensitive to axial stress than a vertical hydraulic aperture and that a vertical hydraulic aperture is more sensitive to confining stress than a horizontal hydraulic aperture. For a single crack model, the sensitivity of a 70⁻90-degree crack to confining pressure is greater than that of a 40⁻60-degree crack. The axial stress sensitivity of a 40⁻60-degree crack is greater than that of a 70⁻90-degree crack. For a typical fracture model, under the same stress conditions, the sensitivity of four typical cracks to confining pressure is greater than that to axial pressure