Fracture evolution law and similarity simulation analysis of overburden movement in long-distance lower protective seam mining

GAO Zhongguo; YANG Junpeng; XIN Yajun; LI Guangzeng; CAO Jianbo; ZHANG Dongying; FANG Yudong; GONG Jiawei

doi:10.11799/ce202505016

Abstract：Long-distance protective seam mining is restricted by the long distance,the insignificant pressure relief effect and the construction difficulty of cross-bed drilling.Taking 9#coal seam(outburst)and 15#coal seam(non-outburst)as background,we adopted theoretical analysis,similar simulation and field test to analyze the characteristics of"two zones"distribution in roof and gas flow law after long-distance protective seam mining,to discuss roof movement of working face and stress distribution law,and designed the mining scheme of long-distance protective seam.The results showed that the pressure relief of protected seam was mainly related to the height development of the"two zones",and the protected seam was in the bending subsidence zone in engineering mine;after the mining of the lower protective seam,"three zones"appeared above the protective seam,the difference between the curves of both sides of cut hole and stopping line were obvious,the subsidence of coal roof was the most obvious,the one near the protected seam roof was moderate,and the one on the upper was obvious;the abutment pressure in front of the working face of the protective seam increased firstly,then decreased and finally increased slowly with working face advancing;the stress of the protected seam increased slowly firstly,then decreased and finally increased slowly with working face advancing;during the mining of the protective seam,the periodic weighting was obvious,and the average caving interval of periodic weighting was 17 m,the fracture development zone formed to trapezoid as working face advance 243 m,the upper caving angle is 69°,and the lower caving angle 62°;9#coal gas could be extracted from the 15#cross-bed drilling,the gas extraction concentration had a slight decline trend with the increase of time,the gas concentration dropped to 3.8%in day 65,and the extraction effect was significant.