Fractal characteristics of acoustic emission events based on single-link cluster method during uniaxial loading of rock

Abstract

A rock mechanics test system and an acoustic emission (AE) test system have been employed to conduct AE event location experiments on sandstone samples under uniaxial compression. According to the single-link cluster (SLC) method, an SLC structure is set up. Each single link is defined as a spatial vector, which can be calculated based on the spatial coordinates of the nearest neighbor of a certain AE event minus the spatial coordinates of this event. Based on the basic theory of fractal geometry, a spherical surface-covering method is proposed herein to analyze the fractal property of spatial vector direction in an SLC structure. To study the change in fractal dimension over time, a sliding event window is used. The results show that the window length and slide step length have little effect on the change in trend of fractal dimension. Before buckling failure of a rock sample, the fractal dimension curve shows a clear downward trend. The reason for the change in fractal dimension is related to the generation mechanism of AE events. Therefore, a clear decrease in fractal dimension can be taken as precursor to rock buckling failure under uniaxial compression. This research provides a new method for studying the evolution process of rock buckling failure and has important significance regarding the monitoring of rock stability and early warning of rock burst.