Research on the migration characteristics of overlying strata and the feasibility of ascending mining in thin coal seam
摘要
To address the key issue that the overlying rock movement characteristics and factors influencing the feasibility of upward mining in the 4−4 coal seam of Yujialiang Coal Mine remained unclear, theoretical analysis was conducted on the temporal and spatial characteristics of coal and rock movement during upward mining of the 4−4 coal seam. Numerical simulation was applied to study the settlement and movement law of the 4−4 coal seam, and borehole peeping was used to explore the factors affecting the feasibility of upward mining for thin coal seams. The results indicated that after the extraction of the 5−2 coal seam, the development height of the overlying rock fracture zone in the goaf ranged from 95 to 120 meters, while the height of the caving zone varied between 9.3 and 21.1 meters. The 4−4 coal seam was situated within the fracture zone, with an average height of 18.76 meters above the caving zone. The settlement curve of the 4−4 coal seam exhibited distinct zoning features. From the coal pillar area to the goaf, the settlement rate changed following the pattern of “small, large, small”. In terms of settlement values, the middle part of the goaf had higher values than the 15-meter range of the coal pillar, which in turn were higher than those in the coal pillar area. The maximum settlement value in the middle of the goaf reached 4.57 meters, and that at the center of the coal pillar was 3.31 meters. The maximum stress concentration coefficient at the coal pillar was 1.24, which was higher than the 0.53 recorded in the goaf. Correspondingly, the vertical stress distribution of the 4−4 coal seam floor had minimal impact on roadway layout. Factors influencing upward mining were analyzed using methods including “two zones” discrimination, ratio discrimination, surrounding rock balance, and mathematical statistics. It was confirmed that the 4−4 coal seam of Yujialiang Coal Mine met the necessary conditions for upward mining. The research findings can provide a theoretical basis for the safe and efficient upward mining of thin coal seams under similar geological conditions..