Abstract: In view of the important influence of fracture development regularity on roof control during coal seam group mining, based on the mining and geological conditions of Songhe coal mine in Guizhou province, the development regularities of rock fractures during mixed-mining of coal seam group were studied by using physical simulation test. Studies show that when using mixed-mining in coal seam group，the development degree of overlying rock fractures is influenced by composite thickness of coal seam, layer distance and mining sequence, etc. In descending mining, the mining of lower seam lead to the ratio of fractured zone height to mining height of the upper seam increasing. In ascending mining, the ratio of fractured zone height to mining height is relatively small after the upper coal seam mining，but the roof fractures in adjacent lower seam may be continuously developed, which making the ratio of fractured zone height to mining height increase. In addition, it show a logarithmic relation between the ratio of fractured zone height to mining height and coal seam composite thickness, while the relation between the fractures developing height and roof convergence shows three degree polynomial relation. The results can provide basis for roof control design in mixed-mining of coal seam group.

Key words: coal seam group, mixed mining, physical simulation, mining-induced fracture, ratio of fractured zone height to mining height