To evaluate the dynamic evolution of the groundwater chemical characteristics in multi-layer aquifers under coal mining conditions, this study takes Qinglong Coal Mine as a typical case for systematic analysis. A comprehensive research method combining hydrochemical analysis and numerical simulation is adopted, coupling MODFLOW, MT3D, and PHREEQC modules to simulate the synergistic changes in the groundwater flow field and hydrogeochemical reaction during coal mining. The results show that among the studied aquifers, the coal seam aquifer (P₃l) has the worst water quality and is most obviously disturbed by mining activities, with its hydrochemical genesis mainly controlled by water–rock interaction. After mining, groundwater depression cones are formed near pumping wells. Fissure development-induced leakage recharge enhances hydraulic connectivity between aquifers. The P₃l aquifer undergoes slight acidification with a significant increase in SO₄²⁻ concentration, while the overlying roof aquifers (P₃c and T₁y) show gentle hydrochemical changes, with ion concentration anomalies mainly occurring at fissure penetration zones. Overall, coal mining not only alters the groundwater flow field but also transforms the underground environment from a reducing to an oxidizing state. Thereby, it significantly affects the groundwater chemical composition in the mining area. This study provides a scientific basis for groundwater environment protection and rational development of groundwater resources in coal mining areas.

Previous studies have shown that stress interactions affect crack closure, yet no work has so far quantified such effects for different crack types. This study introduces an analytical solution for the deformation of elliptical and nonelliptical cracks, excluding stress interactions. A comparison with numerical simulations incorporating stress interactions enables the quantification of deviations attributable to them. Results indicate that stress amplification accelerates crack closure, whereas shielding slows it. The elliptical model is more sensitive to stress interactions than the nonelliptical one, with its closure behavior more strongly affected by crack interactions. In randomly distributed cracked models, nonelliptical cracks exhibit progressive closure due to cooperative major- and minor-axis deformation, leading to greater distance between the cracks and thus effectively attenuating local stress interactions. Therefore, their numerical results agree markedly better with the single-crack analytical solution. For cracks with small aspect ratios (<0.001), both elliptical and nonelliptical cracked models undergo rapid closure, yielding a narrow window for stress interactions and thus a close convergence between actual results and the single-crack reference model.