Characteristics of overburden"three zones"and the optimization of pressure relief gas extraction in roof cutting pressure relief

GAO Xiancheng; CHENG Zhiheng; WANG Peng; CHEN Liang; ZHOU Lijie

doi:10.11799/ce202510012

Abstract：When the gob-side entry retaining by roof cutting technology is applied in outburst coal seams,the poor sealing of the goaf increases the difficulty of gas control in the working face goaf.To address this issue,taking the No.4303 fully mechanized mining face in Shaqu No.2 Coal Mine as the engineering background,the characteristics of overlying strata fissure development in the working face goaf were studied through key strata numerical calculation,FLAC3D numerical simulation,and the double-end sealed segmented leakage detection method in boreholes.Combining with the engineering practice of fissured zone boreholes,the enriched layers of pressure-relieved gas in the goaf were analyzed to determine the optimal extraction layer for directional drilling fields.The research results indicate that after the gas extraction of the No.4 coal seam,large-scale plastic failure occurs in the coal seam roof,which sinks entirely with the maximum subsidence at the center of the goaf.The height of the caved zone in the working face goaf ranges from 10.7 to 12.6 m,and the height of the fracture zone ranges from 32 to 34 m.The rock strata beyond 41.68 m above the roof are in the the bending subsidence zone.Comparative analysis of the gas extraction data from the test boreholes in the roof fissured zone and the original high-level extraction borehole field during the same period shows that the enriched layers of pressure-relieved gas in the goaf of the working face are approximately 17 to 33 m above the coal seam roof.The final hole section of the fissured zone boreholes should be controlled within a vertical height range between 6 to 11 times of the mining height to achieve efficient gas extraction.