Water–Sediment Two-Phase Flow Inrush Hazard in Rock Fractures of Overburden Strata During Coal Mining

To investigate the mechanism of water–sediment inrush during coal mining, the characteristics of water–sediment flow in rock fractures were quantitatively analyzed by computational fluid dynamics (CFD). Based on the two-phase flow theory, a resistance model of water–sediment flow in fractures was established and verified by a laboratory-scale test. The results showed that: (1) With increases sediment particle diameter, volume fraction, and initial water phase velocity, the resistance of sediment particles grows gradually. (2) The drag force of sediment particles is mainly generated from the collision of the water phase and fracture wall. The velocity distribution of sediment particles can be divided into three stages, i.e., continuous increase, rapid decrease, and slow fluctuation. (3) The numerical model was shown to have high predictive accuracy by comparison with the test results. The model’s predictive accuracy decreases with increased water phase velocity and decreases of the sediment particle diameter and volume fraction. (4) The smaller the fracture width, the larger the inclination and bending angles, and the greater the resistance of the two-phase flow in the fracture. Collisions between the particles and fracture wall cause velocity attenuation of the sediment particles. We propose water–sediment inrush prevention and control technology based on the numerical analysis results.