Coal and rock dynamic disasters occur frequently in deep coal mining. The loading rate affects the mechanical properties and behaviors. Uniaxial compression acoustic emission (AE) tests of bump-prone coal under various loading rates were carried out, and the mechanical properties, AE spatiotemporal evolution, and spatial fractal characteristics were analyzed. The experimental results indicate that the uniaxial compressive strength is positively related to the loading rate, and the elastic modulus increases before decreasing with the loading rate. The failure strain is positively related to the loading rate, and the percentage of the compaction phase relative to the pre-peak phase decreases with the loading rate. The hit rate, absolute energy, AE events, and amplitude evolution of coal samples under various loading rates are the same, and the maximum of AE absolute energy and hit rate is positively related to the loading rate. The spatial evolution of AE events of coal samples under various loading rates is the same, showing a “slow increase → slow increase → fast increase → rapid increase → slow increase” trend. The spatial fractal dimension ranges from 2.1 to 2.9, and the evolution of coal samples under various loading rates is the same, exhibiting a downward trend.
During coal mining, the mechanical and deformation behavior of the overburden is affected by water and stress. Therefore, it is of great significance to study the mechanical behavior of the surrounding rock under the action of hydraulic coupling. For high-intensity mining with shallow coal seam and large mining and strong strata behavior in stope, the hydraulic support is often damaged. Based on basic experiments and physical similarity simulations, overburden fracture in shallow coal seam in western mining area under hydraulic coupling was studied. The results show that under the loading rate range of 0.5~5 mm/min, the compressive strength of sandstone increases with the loading rate. The faster the loading rate, the shorter the duration of the rock sample being loaded and damaged, and the fewer the acoustic emission events. The first weighting step of the main roof of the working face is 54 m, the periodic weighting step is 12.75~28 m, and the average periodic weighting step is 22 m. There are only caving zone and fractured zone in the overburden of working face; the height of caving zone and fractured zone is 60 m and 168 m, respectively. The strength of the saturated sample is significantly reduced. During the excavation of the working face, the temperature difference between the fracture and the overburden value is ≥1°C, which can be used as a threshold for judging the development range of overburden fracture in similar simulation experiments.
The coal and rock dynamic disasters occur more and more frequently in deep mining, which is tightly correlated to the instability of coal pillars under high stress and cyclic disturbance load. In this study, the strength, deformation behaviors, and failure mechanism of coal under cyclic loading in a high-stress state were investigated by considering the influence of cyclic loading rate. The experimental results indicate that the compressive strength is positively correlated with the cyclic loading rate, and the deformation patterns, AE amplitude, and spatial evolution are the same under various cyclic loading rates. The damage variable shows the "slow increase→fast increase→slow increase→ fast increase →slow increase→fast increase→rapid increase" trend.The damage growth rate ranges from 9.32 × 10 −5 to 4.86 × 10 −3 , and increases with the cyclic loading rate. The spatial fractal dimensions under various cyclic loading rates are the same, and the distribution ranges from 2.1 to 2.9, showing a general downward trend. The microfailure mechanism under various cyclic loading rates is mixed failure dominated by tensile failure, with a small amount of shear failure. There is a positive correlation between the percentage of shear cracks and the cyclic loading rates.
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