Mechanism and influencing factors of dynamic-static load induced rock burst under the composite effect of key strata

In Ordos mining area, the movement and fracture of adjacent sandstone strata in Zhiluo Formation are prone to interacting with each other to form composite effects, resulting in high peak and wide range of advanced support stress on the working face, as well as frequent large energy micro-seismic events, and different dynamic characteristics under the influence of different composite key strata. Based on the discrepancies in dynamic behavior of different drilling control areas on the 3⁻¹02 working face, a structural mechanics model of thick sandstone key strata composite effects were constructed using theoretical analysis and data analysis methods, the mechanism of rock burst in the stope of composite thick and weak key strata was revealed. The influence of the overlying and underlying strata thickness ratio and the interlayer thickness on the composite effect of rock strata was simulated, and the energy release and load reduction scheme under the action of composite effect was optimized. The results show that the discrepancies in the occurrence state of key strata near the coal seam is the fundamental reason for the difference in dynamic behavior. The rock burst hazard in areas with two sandstone strata with a thickness of more than 30 m is higher than that in areas with a single layer of 50−70 m. The formation conditions of composite key strata are proposed: the two key strata move synchronously and have no shear slip at the strata interface and maximum shear stress in the model. Under the composite effect of key strata, the peak stress and range of advanced support increase, with the strong dynamic load released by rock fracture, which is basically consistent with the on-site data, confirming that the rock burst under the composite effect of key strata is induced by the superposition of static load and multiple strong dynamic loads. The closer the thickness of the overlying and underlying and the thinner the thickness of the interlayer, the stronger the composite effect between the rock strata. After the optimization of deep hole blasting in the roof and large-diameter drilling in the coal seam, the intensity of large energy micro-seismic events activity on the working face and the concentration of stress in the coal-rock mass are significantly reduced, effectively weakening the composite effect of key strata on the rock burst hazard.