DEM-CFD coupling analysis of broken rock mass movement in underground reservoir of coal mine

The construction of an underground reservoir in the mine goaf is beneficial to the coordination of coal mining and water environment protection and utilization. The caving zone in the goaf is used as the coordinated bearing body and storage volume of the mine underground reservoir. The transportation and removal of the internal broken rock mass during the circulation storage and discharge of the underground reservoir directly affect the porosity distribution and seepage characteristics, and may also cause the pipe to be blocked. Based on the engineering background of underground reservoir water storage, this paper constructs a fluid-solid coupling model of mine water seepage in broken rock mass model, and quantitatively analyzes the influence of porosity of caving zone, radius of broken rock mass and fluid velocity on fluid pressure and migration of broken rock mass. On this basis, the DEM-CFD coupling numerical simulation of the broken rock mass model with different fluid flow rates was carried out. The results show that: the fluid pressure on broken rock mass in the process of water seepage is composed of drag force and gradient force, and the gradient force can be ignored in the background of mine reservoir engineering. The increase of porosity in the caving zone makes the fluid pressure decrease sharply. The results show that the influence on the movement of broken rock mass is small in the range of porosity in the caving zone. The fluid pressure increases in a power function with the increase of the particle size, but the increase of the particles also increases the gravity, which greatly increases the fluid pressure required for the movement of the particles, and the smaller the particles, the easier it is to be carried by the fluid. Due to the contact stress between particles, it is difficult for the fluid to break the original equilibrium structure. Only the small particles free in the pores of the broken rock structure can be carried by the fluid, which has little effect on the porosity of the overall broken model. The research results are helpful to scientifically evaluate the evolution of porosity in the caving zone during the storage and discharge of underground reservoirs. © 2021, Editorial Office of Journal of Mining and Strata Control Engineering. All right reserved.