象山矿上保护层开采卸压保护范围研究OA

To address the technical challenges of sparse monitoring points in the protective range and significant errors in determin-ing protection boundaries during close-distance upper protective seam mining,this study takes the 21311 working face of Xiangshan Mine as the engineering background.By integrating FLAC3D numerical simulation with field multi-borehole joint measurements,a systematic analysis was conducted on the spatiotemporal evolution of the stress field,plastic zone,expansion deformation,and per-meability of the protected seam during upper protective seam mining.The effectiveness of gas control measures was also evaluated to achieve precise delineation of the pressure-relief range and optimization of the monitoring method.The results indicate that the floor stress field evolution exhibits a three-stage characteristic:"local pressure relief-symmetrical expansion-steady-state balance".The maximum vertical stress reduction in the pressure-relief zone reached 95%of the original rock stress.The plastic zone expanded in a"trapezoidal"pattern,with a maximum failure depth stabilized at 30 m,ensuring the protected seam entered a fully fractured and pressure-relieved state.The expansion deformation rate and permeability showed a"saddle-shaped"symmetrical distribution,with the permeability in the core pressure-relief zone increasing to 172.5 times its original value,providing favorable channels for ef-ficient gas drainage to optimize the field monitoring approach,20 boreholes were strategically arranged along the strike(Group A at the open-off cut side and Group D at the final line side)and dip(Group B at the auxiliary intake airway side and Group C at the main intake airway side)for intensive monitoring.Based on the critical expansion deformation rate index,the pressure-relief angles were accurately determined as 61° at the open-off cut side,58° at the final line side,79° at the auxiliary intake airway side,and 81° at the main intake airway side,significantly improving the accuracy of boundary identification.In combination with directional long bore-holes in the floor for intercepting and extracting downward pressure-relief gas,the maximum gas extraction rate reached 55.31%.The residual gas content in the protected seam was reduced to 2.29-3.90 m3/t,the permeability coefficient increased by 8-12 times,and the borehole gas flow decay coefficient decreased by approximately 40%-50%.