Distribution characteristics of"similar cooling tower"in gas migration and storage areas of inclined extremely thick coal seam and sub-domain extraction method

ZHAO Pengxiang; ZHUO Risheng; LI Shugang; SUN Xueyang; LIN Haifei; LIU Yuanjia; CHANG Zechen; YANG Junsheng; ZHANG Yibo; SHAO Qiudong

doi:10.13247/j.cnki.jcumt.20250243

Abstract：To explore the distribution characteristics of the fracture field and the law of pres-sure-relief gas storage and migration in the goaf under the condition of fully mechanized top coal caving mining in an inclined extremely thick coal seam,and to study the optimization mechanism of gas extraction methods,a large-scale two-dimensional physical similarity simu-lation experiment was carried out in a gassy coal mine.The movement form of overlying strata in the stope was analyzed,the stress evolution characteristics of the overlying strata were ob-tained,the displacement,angle,and probability entropy change characteristics of the overly-ing strata were calculated.The formation mechanism of"similar cooling tower"in pressure re-lief gas transportation and storage area was clarified,the development form of gas transporta-tion and storage area was deduced,the mathematical theory control model of gas transporta-tion and storage area was constructed,and the pressure relief gas drainage technology was pro-posed.The results show that under the condition of fully mechanized caving mining in an in-clined thick coal seam,the pressure-relief gas transportation and storage area exhibits a"cool-ing tower"distribution pattern.The maximum stress change value in front of the coalwall side of the transportation and storage area is 37 MPa,and the stress concentration coefficient is 7.60.The bulking coefficient of the overburden rock shows an asymmetric distribution charac-teristic of"high on both wings and low in the middle",and the bulking coefficient increases from 1.19 to 1.61.In addition,PCAS image analysis software was used to obtain the distribu-tion law and spatial relationship of voids and cracks.The development degree of the crack structure on the open-off cut side is significantly more complete than that on the working face side.A fractal dimension of 1.28 and a crack length of 15 mm are defined as the judgment pa-rameter indexes of the pressure-relief gas transportation and storage area.Considering the mi-gration,diffusion,and reservoir form of gas in the goaf,a mathematical theoretical control model of the pressure-relief gas storage area in the inclined thick coal seam was established,and a boundary calculation formula for the pressure-relief gas storage area was derived.This model guides the design of the layout parameters of high-level directional long boreholes and has achieved favorable extraction results.The research results have been preliminarily applied in the Liuhuanggou coal mine,which provides a theoretical reference for the efficient extraction of gas in fully mechanized caving mining in inclined extremely thick coal seam and ensures the safe and efficient mining of mines under similar conditions.