Application of microseismic monitoring in the optimization of control strategy for roofs composed of composite hard sandstone masses

With a gradual increase in the coal mining depth in China, the movement of overlying thick and hard rock layers exerts increasingly complex impacts on the mine pressure. In the Ordos area, the overburden of the mining face of most mines hosts composite hard sandstone masses, serving as key layers characterized by considerable thicknesses, high hardness, and close proximity. As a result, the risks of mine earthquakes and dynamic manifestation co-exist in the mining face. With the roof of mining face11-3106 in a coal mine within the Ordos mining area as the engineering background, this study investigated roofs composed of composite hard sandstone masses. Based on the evolution of microseismic accumulation characteristics and using methods like theoretical analysis and numerical simulation, this study investigated the breaking-induced fracture development in the roofs and explored the control measures for the roofs. The results indicate that as the mining face advanced, the overlying composite hard sandstone masses broke in the zone with significant microseismic accumulation. The breaking positions can be identified based on the evolutionary patterns of microseismic accumulation characteristics. The high-density microseismic accumulation zone in the mining face manifested high microseismic frequency and energy, accompanied by regional peak high-energy events. As mining face 11-3106 advanced to the first and second square states (i.e., the first advancing distance of the mining face equals its length, and the second advancing distance of the mining face equals twice its length), the breaking characteristics of the composite hard sandstone masses exhibited two to three small cycles and a large cycle, with dynamic microseismic accumulation occurring along the strike of the mining face. The breaking span for deep-hole pre-splitting blasting was optimized based on the evolutionary characteristics of microseismic accumulation, significantly reducing microseismic accumulation in the air-return roadway and the mining influence range. The control measures for the roof composed of composite hard sandstone masses were optimized based on the dynamic migration of composite hard sandstone masses derived using the microseismic accumulation in the mining face. This study can serve as a reference for controlling the mining face roofs with similar overburden structures in the Ordos mining area.