Surrounding Rock Activities Laws Under Composite Key Layer of Overlying Thick Bedrocks in Shallow Buried Deep Coal Seams

Surrounding rock stress and roof bracket force is unique during process of mining face under multiple layers composite effect. In this paper, Changhangou Mine is used the study of surrounding rock activities laws under composite key layer of overlying thick bedrocks in shallow buried deep coal seams. It is determined by critical layer theory that fine sandstone of 19 m above the working face is sub-critical layer and 47.5 m coarse sandstone at the top is main key layer. Overburden law is achieved by RFPA numerical simulation results that sub-layer and the primary key critical layer control overburden movement, destroy and remove of overburden is characteristic of "two belts" .Through the support load monitoring, we receive that stope pressure exhibits heterogeneity cycle, sub-layer key breaking causes little cycle pressure, and the main key stratum breaking cause large cycles pressure.