Study on energy consumption and failure mechanism of water-saturated coal sample during impact cracking

To uncover the mechanism of energy dissipation in coal samples when subjected to both water and dynamic load, the damage patterns and energy absorption properties of coal samples in their natural and saturated states were investigated and analyzed through Hopkinson impact experiments. The results of the study show that the mass and wave velocity of the natural coal samples show an increasing trend when they are saturated with water. And the mass and wave velocity increase by 6.35 % and 21.42 % respectively. The coal sample's level of fragmentation and dynamic strength exhibited a positive correlation with the velocity (1 m/s-5.69 m/s) of impact. When subjected to dynamic loads, both natural and water-saturated coal samples primarily undergo splitting, fracturing, and crushing. Compared with natural coal samples, saturated water coal samples show greater degree of crushing and lower mechanical strength. The dynamic strength of saturated coal sample at 5.25 m/s (15.66 MPa) decreased by 33.86 % compared with that at 5.69 m/s (23.68 MPa). The mean size of particles in coal samples, both in their natural state and when saturated with water, had an linear reduction relationship with impact speed. Conversely, the fractal dimension, which represents dissipation, had a direct relationship with impact speed. The fractal dimensions of dry and saturated coal samples are distributed in the ranges of 1.56–2.08 and 1.65–2.1, respectively. And the dissipative energy of natural coal samples between 1.09 m/s and 5.67 m/s is about 0.039 J/cm³-0.175 J/cm³, and that of saturated coal samples between 1 m/s and 5.25 m/s is about 0.034 J/cm³-0.088 J/cm³. The surface energy of coal samples was analysed and calculated, and an energy consumption prediction model was proposed to predict the energy consumption of coal samples after dynamic crushing.