Analysis of Fractal Characteristic of Fragments from Rock Burst Tests under Different Loading Rates

Original scientific paper Rock burst is a common serious geological hazard in underground engineering, which seriously affects the progress of projects. The mechanism of rock burst can be explained by the distribution law of rock fragments and its fractal characteristics. A simulation experiment of rock burst was conducted with the granite samples under a biaxial loading machine system to analyze the fractal characteristics of the fragments from rock burst tests. The granite fragments were collected and divided into coarse, medium, fine, and micro grains by a screening method. The number and mass distribution of the fragments in different size ranges were also analyzed. The fractal dimensions of the rock fragments were calculated by the mass-granularity distribution method. Results show that the loading rate is proportional to the damage degree of rock burst; the mass of rock burst debris increases with the increase in loading rate, which indicates that a high loading rate leads to considerable rock damage. A high loading rate also results in small proportions of fine and medium grains and a large proportion of coarse grain, with no significant change in the micro grain. Under the high-loading-rate condition, the fractal dimensions of rock fragments are small, but the released energy of rock burst is large. The conclusions obtained in this study confirm the feasibility of reducing the risk of rock burst by adjusting the excavation rate in engineering practice and provide the basis for further study on the mechanism of rock burst.