Water inrush mechanism of coal mine shaft fracture under fluid-solid coupling

The occurrence of coal mine shaft fractures and water inrush accidents is alarmingly frequent, endangering the lives of underground personnel and compromising mine safety. To comprehend the influence of confined groundwater in the process of shaft fracture and the formation mechanism of water inrush channels, a model test was devised using similarity theory and coupled fluid-solid numerical simulation technology. The findings reveal that direct contact between the shaft lining and pressurized water hinders the development of load-bearing and deformation capacities. This is specifically evidenced by the premature appearance of the yield point, a reduction in peak strength and strain, and a broader distribution of macro cracks. These effects result from the coupling interaction between the seepage field and stress field induced by the penetration of pressurized water into the concrete lining of the shaft. Numerical simulation analysis based on the model test results yields a set of parameters for calculating shaft fractures under fluid-solid coupling conditions. Subsequently, a meso-numerical analysis of shaft fracture and water permeability processes is conducted under different pore water pressures: 0.05, 0.10, 0.20, and 0.40 MPa. It is observed that an increase in pore water pressure leads to a reduction of 5.88%, 17.65%, and 23.53% in the critical lateral load on the shaft, respectively. Internal crack development near the yield strength of the specimen is notably accelerated, with cracks expanding continuously and eventually forming permeable channels that connect the interior and exterior of the shaft lining. The water inrush channel first emerges under a pore water pressure of 0.40 MPa, which is 2.67, 2.53, and 1.67 times earlier than the other three pore water pressures. This indicates that higher pore water pressure corresponds to a faster crack growth rate, with the crack initially propagating radially before transitioning to a circumferential path. Acoustic emission monitoring demonstrates a gradual increase in the number of events leading up to the occurrence of shaft fracture, followed by a sustained high level of activity. Once the water inrush channel is formed, stress is relieved, resulting in a sharp drop in the frequency and number of acoustic emission events. This characteristic can serve as a basis for on-site monitoring of water inrush from shaft fractures, which providing evidence for the prevention and control of water inrush as well.