EXPERIMENTAL STUDY ON FRACTAL DIMENSION CHARACTERISTICS OF ACOUSTIC EMISSION OF ROCK UNDER MULTILEVEL UNIAXIAL CYCLIC LOADING

Experiments on acoustic emission (AE) characteristics of fractal were carried out under uniaxial multilevel cyclic loading. AE rate, energy rate and spatial distribution of different rock specimens were obtained. Relevant fractal dimensions of AE rate and energy rate were figured out through G-P algorithm based on the theory of reconstruction of phase space. Relevant fractal dimensions of AE spatial distribution was figured out through column-covering method. The results show that AE rate, energy rate and AE spatial distribution are of fractal characteristics,and among them, AE spatial distribution has the most obvious fractal characteristics. Phase space has some effects on relevant fractal dimensions, and it is better to choose 4 as the basic dimension for correlation dimension calculation. The comparison of development trend of AE spatial distribution and relevant fractal dimensions under different cycles shows that fractal characteristics can reflect the statistical evolution of the micro-cracks in rock. Relevant fractal dimension increases under isobaric cyclic loading and decreases with the increasing of stress. Relevant fractal dimensions fluctuate in a small range or decrease slowly when the higher stress has been reached. The characteristics above can be used as the reference for micro-seismic monitoring warning on ground pressure in mining.