Strong strata pressure caused by hard roof group structure breaking and supporting strength determination

A comprehensive research method composed of theoretical analysis, physical simulation and engineering practice was conducted to analyze the impact effect caused by thick hard roof group structure breaking. Some results were obtained such as the main influencing factors related to impulsion pressure, the main roof weighting characteristics and the reasonable supporting strength of the roof group structure. It is shown that impact load caused by layered hard roof group structure breaking will lead to severe concussion with scarcely attenuation. The roof weighting on the workface is affected by a combined effect of dynamic load and static load resulted from layered hard roof group structure breaking. The impulsion pressure strength is associated to roof thickness, rock traits, and rock joints and weak surfaces. For the similar roof strata, the impact effect is more severe as the roof is thicker, but the thick caving roof will be helpful for buffering the impact of the upper overburden strata. A field test was conducted in Datong area which is mining under the hard roof group structure. According to selecting the high strength supports of ZF15000/28/52 in the fully mechanized caving face to ensure safe mining before and after the first critical roof breaking, and taking the auxiliary control of hydraulic fracturing in the upper critical roof, the strong pressure has been effectively slowed.