Study On Pressure Relief Technology Of High Pressure Water Jet Of Residual Coal Pillar In Overlying Goaf In Close Seam Mining

Based on the geological occurrence of 3#coal seam and 4#coal seam in Yanzishan Coal Mine,this paper adopts theoretical analysis,numerical simulation and field practice to study the pressure relief technology of high-pressure water jets for residual coal pillars in overlying goaf in close seam mining.Under similar conditions,the safe mining of close-seam coal seam mining provides safety guarantee and theoretical guidance.The main research results are as follows:(1)According to the theoretical analysis and FLAC3D numerical simulation,the bearing load and elastic core area of the residual coal pillar are obtained;The calculation model of concentrated load above the residual coal pillars is established,revealing that the vertical stress plays a leading role in the process of stress transmission on the floor.(2)Fluent numerical simulation was used to study the change rule of nozzle axial velocity and axial dynamic pressure under different parameters to determine the optimal nozzle parameters.Ls-dyna numerical simulation was used to study the effect of water pressure on coal impact damage and crack propagation.(3)Based on FLAC3D,the models of "single hole single slot" and "single hole double slot"are established to study the change rule of stress and plastic area of coal around the slot with different parameters,and the best slot geometry parameters are obtained when hydraulic cutting the slot on site.(4)Through the mechanical model of hydraulic slotting of residual coal pillar and the model of "double drilling and double slotting",the on-site process parameters are determined and implemented,and the slotting effect is tested by the coal output of single slotting and the monitoring data of hydraulic support of working face.