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In order to study the formation mechanism and evolution laws of gas flow channel in mining coal and rock, using relevant theories of fracture mechanics and rock mechanics with combinations of mining coal and rock's crack development characteristics, the gas flow channels in mining coal and rock ahead of working face were divided into isolated channel area, tensile fracture failure area, shear failure area,and failure area after abutment pressure peak. And according to the developmental process of crack in mining coal and rock and formation mechanism of gas channel in different areas, it's concluded that the first three areas belong to mesoscopic channels, and the fourth area belong to macroscopic channels. According to the relevant theories of material mechanics and deformation and mechanics characteristics of coal roof, crack developmental process and channel conduction property during mining process, roof macroscopic gas channels were divided into three areas from above to below; gas turbulent channel area, gas transition flow channel area and gas seepage channel area, and combined with simulation in laboratory, the development process of gas channel in overlying coal (rock) seams were analysed, which experienced the process of decompression, instability, crack initiation, mutation splitting, anastomosis contraction, accelerated closed, channel preservation, accelerated closed again and compaction closed completely. [ABSTRACT FROM AUTHOR]

For studying the regularity of strata behavior in mining face in thin bedrock with thick surface soil, the stability of structure of main roof were analyzed based on Lijiahao Coal Mine, and numerical simulation software UDEC was used to analyze the regularity of strata behavior in mining face under different ratio of rock and loadings, combined with field measurement of mining coal, block degree of rock i and ratio of rock and loadings were separately put forward to judge the stability of structure of main roof. It was considered analysis that the three-hinge arch structures formed after main roof breaking and the monoclinic structure formed after contacting waste rock of main roof will occur sliding instability when the block degree of rock i is more than 0.40 and less than 1.57; overburden also takes place sliding instability phenomenon easily when first weighting or periodic weighting of the main roof comes; key strata represents sliding instability in thin bedrock with thick surface soil, while it is not large of the ground pressure of regional in front of coal wall when the roof weighting comes; during the roof weighting coming, the regularity of strata behavior in thin bedrock with thick surface soil is that main roof cuts and splits along the coal wall, and emerges roof steps, the dynamic load action on face shield comes obviously. [ABSTRACT FROM AUTHOR]