Study on Space-Time Distribution Characteristics of the Acoustic Emission Sources in Granite Strain Rockburst Experiment

During the rockburst experiments on three granite specimens, a multi-channel acoustic emission (AE) system with location function was adopted to obtain the data of AE sources. Moreover, the space-time distribution characteristics of AE sources have been analyzed quantitatively based on the fractal theory. The results show that the location distribution agrees with the failure results. The spatial fractal dimension of AE sources varies from 2 to 3 at each experiment stage and presents the complicated nonlinear variation trend. At the initial loading stage, the initial cracks in the specimen are closed, leading to a large spatial fractal dimension. Then, the specimen is in a stable state, and the number of AE sources is small, so the spatial fractal dimension decreases. During increasing the vertical stress after unloading suddenly, the micro-cracks develop rapidly, the AE sources are distributed discretely, and the fractal dimension value rises to the peak. As the vertical stress approaches the peak value gradually, many macro-cracks are formed. The number of AE sources increases and presents concentrated distribution characteristics causing the fractal dimension value to descending rapidly. This study would deepen understanding of the rockburst process and can also be referred to provide some indexes for rockburst prediction.