Abstract
In Datong mining area, CO and other harmful gases were discharged from the gob in the Jurassic overburden strata to the panel of Carboniferous coal seam. To this end, panel 8309 of Tongxin coal mine in Datong mining area was taken as the engineering background; the change law of CO concentration in the upper corner of the panel and the law of mining pressure were studied through field measurement, and the influence of periodic movement of key strata on the downward leakage law of harmful gases was analyzed. In this paper, the fracture law of the key strata and fracture development characteristics of overburden strata were further studied by the similar simulation test, and the influence of the periodic movement of the key strata on the pathway formation of gas downward leakage was analyzed. The results show that the main cause of harmful gas downward leakage in the Jurassic gob is through the fracture produced by the fracture of the higher key strata. If the higher key strata fractures in the coal mining in the Carboniferous system, through fracture connecting the Jurassic gob above the open-off cut and the upper part of the panel are formed, and effective pathways for gas downward leakage are generated. The fracture and rotation of the higher key strata are accompanied by the formation and disappearance of the effective pathway for gas downward leakage above the panel. Then the periodic change of harmful gas discharging to the panel is caused and consistent with the law of mining pressure.
Highlights
Datong mining area has both Jurassic and Carboniferous coal seams
Fractures are interacted with the gob in Jurassic coal seam and Carboniferous coal seam; and the downward leakage of harmful gases can be caused from the Jurassic gob, which seriously affects the safe and efficient mining of the Carboniferous coal seam [4]
The downward leakage of harmful gas in the Jurassic gob is mainly caused by the mining-induced fracture in the interval strata of the dual-system coal seam
Summary
Datong mining area has both Jurassic and Carboniferous coal seams. At present, the upper Jurassic coal resources are almost exhausted, and the lower Carboniferous ultra-thick coal seam has become the main coal seam for the mining [1, 2]. Many scholars have studied the development law of overburden breakage characteristics and mininginduced fracture in overburden strata, and the mining thickness of coal seam is below 8 m [32, 33]. The research on the development law of overburden breakage characteristics and mining-induced fracture in Datong mining area should be carried out systematically. The key strata theory has been well applied in the development law of water-conducting fracture zone and the mining-induced fracture evolution related to gas drainage. The influence of the periodic movement of the key strata on the gas downward leakage pathway and gas drainage law was analyzed, so as to ensure the safe and efficient mining of the dual-system coal seams. This study provides a theoretical guidance for coal mining in the dual-system coal seam
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