本煤层顺层预抽钻孔采掘扰动影响下漏风模型的建立及分析OA

Bedding pre-drainage boreholes in the coal seam are an important measure to reduce coal seam gas content.In the later stage of gas drainage,affected by mining disturbance,the fractures in the coal mass around boreholes gradually become interconnec-ted,which leads to a significant increase in air leakage,further resulting in a decline in gas drainage concentration and seriously re-stricting the effect of gas control.To deeply study the air leakage law under the disturbance of mining and excavation for the bed-ding pre-drilling holes in this coal seam and solve the problem of low gas concentration in the holes during the later stage of extrac-tion,the 15305 working face of Liyang Coal Mine in Shanxi Province was selected as the study site,a borehole air leakage model under mining disturbance was established using COMSOL multiphysics simulation,and the evolution of gas pressure fields and air leakage flow under different extraction times,sealing lengths,and negative pressure conditions was systematically analyzed.The simulation results were further validated through field tests.The results show that with prolonged extraction time,coal fissures gradually develop and interconnect,and air leakage significantly intensifies,the minimum sealing depth extends beyond the plastic zone affected by roadway excavation and reach near the elastic zone;field tests confirmed that the reasonable sealing length is 15 m.In the later stage of drainage,when the negative pressure of bedding boreholes was reduced from 19-23 kPa to 10-13 kPa,the aver-age gas volume fraction increased from 2.98%to 6.38%,demonstrating a clear improvement in drainage efficiency.Based on these findings,a dynamic gas control mode of"two increases,two extractions,one blockage,and one change"was proposed,which integ-rates"mechanical and hydraulic permeability enhancement,directional and bedding extraction,optimum sealing length,and dynam-ic negative pressure control".This mode achieves effective spatio-temporal coordination of gas drainage and improves gas concentration,providing theoretical guidance and engineering practice for efficient gas control in high-gas and low-permeability coal seams.