Evolutionary mechanisms and control strategies for surrounding rock stability of inclined shafts under groundwater seepage

BackgroundThe western coal mining area has emerged as China’s primary coal production base. In this area, multiple ten-million-ton-scale coal mines are constructed using inclined shafts. Since inclined shafts run through multiple aquifers, many of them are subjected to shaft wall rupture and water inrushes to varying degrees.Methods This study aims to determine the impacts of groundwater seepage on the surrounding rock stability of inclined shafts. Using field survey, theoretical analysis, and numerical simulation, this study investigated the shaft wall stability of the main inclined shaft in water-rich sections in the Xiaojihan Coal Mine.Results and Conclusions Theoretical analysis revealed the evolutionary patterns of the plastic zone in the surrounding rocks before and after water immersion-induced weakening under different polar angles and the combined effect of supports and pore water pressure. The results indicate that the plastic zone exhibited an approximately butterfly-shaped pattern, proving large in polar angle ranges of 0°‒45°, 135°‒225°, and 315°‒360° but small in polar angle ranges of 45°‒135° and 225°‒315°. Moreover, the radius of the plastic zone increased from 5.8 m to 8.0 m due to the water immersion-induced weakening. To elucidate the mechanisms behind water-induced degradation of the shaft walls and surrounding rocks, a fluid-solid coupling model for water immersion-induced weakening was established. With a decrease in the shaft wall strength, the plastic zone in the shaft cross-section expanded and was connected to the aquifer. Then, water from the aquifer further weakened the surrounding rocks of the shaft, significantly increasing the range and deformation amplitude of the plastic zone and ultimately leading to shaft wall instability. For inclined shafts running through aquifers, grouting schemes under different shaft wall strengths were proposed. The grouting effects were simulated by modifying the mechanical parameters and permeability coefficient of the surrounding rocks within the grouting zone. The simulation results demonstrate that grouting reinforcement can significantly enhance the stability of the inclined shaft wall by increasing surrounding rock strength and sealing aquifer fractures. Finally, the grouting reinforcement and water blocking schemes proposed in this study were applied in the field, significantly reducing water inflow.