A Study of Potential Water–Sand Inrush Based on Physical Model Experiments and Numerical Simulations

A comprehensive study was conducted at three coal mines with thin bedrock zones to understand the occurrence of water–sand inrush accidents in overlying rock strata induced by the combined effects of ground stress generated by the loading of a thick loose layer, secondary mining-induced stress, and bottom aquifer pressure. This study involved field sampling at the Yangcun, Xinglongzhuang, and Baodian coal mines through underground drilling, as well as particle size and microscopic analysis, laboratory model experiments, and numerical simulations. The clay and sandy gravel layers in the lower group of the Quaternary strata in the study area were found to be interlaced. Particle size analysis and microscopic testing of the soil samples had consistent patterns, revealing the compositional structure of the soil samples. The composition structure of the bottom aquifer of the three sampling boreholes differed; using a self-designed experimental device, water–sand inrush tests were conducted with different crack widths. The critical hydraulic gradient decreased with increasing crack width, while it increases with increasing clay content, showing a good correlation; The PFC 3D software was used to simulate the process of water–sand inrush under the influence of mining. The simulation and model testing indicate that water–sand inrush is more likely to occur, the process of water–sand inrush will be more intense, and the duration will be shorter when the inclination angle and crack widths are larger.