Analysis on Failure Behavior of Overlying Strata in Large Cutting Height Workface About Shallow-Buried Coal Seam Under Thin Base Rock

According to special geological structure condition of shallow-buried coal seam under thin base rock in the Northwest of China, failure behavior and migration rule of overlying strata during large cutting height exploitation process were analyzed with numerical simulation based on field measurement. The results show that in large cutting height exploitation process, surface subsidence is not obvious at first, the subsidence of overlying strata is tip-bottom "bowl shape" in non-full mining and it is flat-bottom "discoid shape" in full mining. Due to land surface is loose conglomerate bed and does not have the bearing capacity, the land surface is firstly tensile failure and gradually transforming into shear failure with mining. During large cutting height workface mining, the migration rule of overlying strata is roof abrupt breaking in time domain and roof breaking extension to surface ground in pace domain, and the subsidence rule of surface ground is "saw tooth shape" fracture zone at ground.