Numerical Simulation of the Fluid–Solid Coupling Process During the Failure of a Fractured Coal–Rock Mass Based on the Regional Geostress

Abstract

This paper presents a numerical approach to the simulation of fluid–solid coupling during the failure of a fractured coal–rock mass taking into consideration the regional geostress characteristics. We use the back calculation method to calculate the regional geostress of the study area, and we verify the accuracy of the back calculation method based on the in situ monitoring data. The values of the vertical stress and the minimum principal horizontal stress used in the numerical simulation are 7.057 and 8.085 MPa, respectively. In addition, the maximum principal horizontal stress has a local undulation that is affected by excavation disturbance. With a newly developed mechanical experimental system for digital radiography scanning, the temporal–spatial evolution of the fracture field is also revealed. The main fractures continue to propagate with increased external loading, and the spatial form of the fracture fields is a conjugate pattern and an X-shaped pattern. Based on the COMSOL Multiphysics program, the results indicate that the primary reason for crack propagation and connection is increased external loading, which leads to macroscopic fracturing of the coal–rock mass and incremental changes in the average porosity and permeability. The flow within the maximum velocity region represents the distribution characteristics of the induced cracks. The peak flow velocity is located at the main fracture, and its direction is parallel to that of the water injection pressure. Smaller fractures have a larger hydraulic gradient and larger flow velocities than larger fractures. The water outlet velocity characteristics indicate that the maximum flow velocity in the water outlet is located on the two sides of the model and increases with increasing external loading. All the fluid–solid coupling mechanisms would provide a reliable theoretical basis for optimization of mined-void roof weakening in mining the steeply inclined coal seam.