Mechanical Failure Characteristics and Energy Dissipation Laws of the Coal–Concrete Combination under Impact Rates

Abstract

Mining shallow coal seams and deep coal seams is obviously different. In the deep environment of a coal mine, the stress concentration degree is high, and the dynamic load with impact tendency is prominent. In the practice of underground mining engineering in coal mines, the common coal–concrete combination structure has different degrees of damage and failure under the continuous action of dynamic load at different impact rates, which in turn affects the overall stability of the engineering structure. Therefore, it is of great significance to study the mechanical failure characteristics and energy dissipation law of coal–concrete combinations under the influence of impact rate. In this paper, the split Hopkinson pressure bar (SHPB) dynamic load test system is selected, and coal–concrete combination samples are taken as the impact compression test object. Comparative tests under different impact rates are carried out, and the experimental results of the mechanical parameters of the sample change with the impact rate are obtained. Fractal theory and energy dissipation theory are introduced to study the macroscopic failure characteristics of the combination sample after impact dynamic load and the energy dissipation law during the impact process. The results show that the sample has a strong strain rate correlation, and its dynamic compressive strength, dynamic elastic modulus, and impact rate also have a strong positive correlation. The dynamic stress–strain curve conforms to the four typical stages of the dynamic stress–strain curve. The degree of fragmentation of the sample is proportional to the impact rate. The larger the impact rate, the smaller the proportion of large particle size to small particle size; the fractal dimension of particle size also increases with the impact rate. The transmitted energy, reflected energy, dissipated energy, and incident energy increase with the impact rate, but the increase amplitude is different. The overall energy value is reflected energy > transmission energy > dissipated energy. The energy ratio of different forms fluctuates with the impact rate, the reflected energy ratio is positively correlated with a certain impact rate, the transmission energy ratio is basically symmetric and fluctuates between 30% and 40%, and the dissipated energy ratio increases with the impact rate.