FRACTAL CHARACTER AND MECHANISM OF ROCK BURSTS

Rock bursts are a potential hazard to mine structures and underground personnel. Many studies have been conducted to understand the causes of rock bursts and to predict their occurrence, however, few successes have been achieved. In this paper, the associated microseismicity of rock bursts is studied by using fractal geometry and damage mechanics. Based on the number-radius relation of fractals, the distributions of previously reported micoseismic event locations were examined and found to have a fractal clustering structure. The degree of clustering of microseismic events increases with the approach of a main rock burst that corresponds to a decreasing fractal dimension. The lowest fractal dimension is generally produced near the occurrence of a rock burst. Thus, the fractal dimension has potential use as a rock burst predictor. In seismology, this fractal nature of rock bursts is consistent with the conclusion of a lower fractal dimension (or b-value) being associated with the occurrence of a main earthquake. The fractal and physical mechanisms of rock bursts are analyzed in theory using damage mechanics and the fractal concept. A strong failure (a rock burst, or an earthquake) is seen as equivalent to a fractal cluster of crackings within the rock mass. The energy release E of a fractal cluster of crackings within the rock mass increases exponentially with a decrease of the fractal dimension D in the form: D = C1 x exp[-C2E]. Thus, the fractal nature of rock bursts and earthquakes is well-explained in theory, and a better understanding of rock bursts is obtained.