Abstract
It is very important to study the influence of water content on the mechanical properties of coal rock to prevent rock burst and roadway instability under dynamic disturbance. In this study, the split Hopkinson pressure bar (SHPB) test system was applied to conduct three-dimensional dynamic and static impact tests on natural and water-saturated coal samples at different strain rates to determine the dynamic mechanical properties of a series of water-bearing coal samples. Based on the new data, we discuss the strength, deformation, crushing energy dissipation, and fractal characteristics of natural and saturated coal rocks. We specifically focus on the different effects of hydraulic pressure on crack propagation under static and dynamic loads. Our results document a well-defined linear relationship between the peak stress and the strain rate of coal in the natural state and the water-saturated state. Once the impact rate reaches a certain value, a double peak phenomenon is observed, and the curve shows a certain leap. The critical impact velocity of the curve leap is ca. 9.485~10.025 m/s. At the same strain rate, the average peak stress in the water-saturated state is ca. 2.684% higher than that in the natural state. The secant modulus of the two states generally increases with the rise in strain rate, but the scatter of the results is large. The average secant modulus of the water-saturated coal sample increases by 2.309% compared with the natural state. The energy consumption density and absorbed energy of saturated and natural coal samples rise with the increase in strain rate, and both show a well-defined power−function relationship. However, under the same condition, the absorbed energy and absorbed energy density of water-saturated coal samples are higher than that of natural coal samples. The fractal dimension of water-saturated coal rises with the increase in strain rate and energy consumption density, showing a strong linear and quadratic relationship, respectively. Under dynamic loading, the cohesive force, jointly generated by free water and the Stefan effect, hinder the expansion of coal and rock fractures, thus improving the compressive strength of coal and rock. The study provides a reliable theoretical basis for preventing rock burst and providing roadway support.