单轴多级循环加载岩石声发射分形特性试验研究

通过对三种岩石试样进行单轴循环加载试验,获得岩石试样加载过程中声发射事件率、能量率和空间位置分布数据。运用相空间重构理论直接从时间序列上通过G-P算法求得事件率和能量率关联分维,根据柱覆盖法求解得到声发射事件源空间分布关联分维。研究结果表明,声发射事件率、能量率和空间分布都具有分形特性,且声发射源空间分布分形特性最为显著。相空间的选取对关联维数有一定影响,相空间取值为4时能够较好地计算关联维数。将不同加卸载循环声发射源空间分布的变化趋势和声发射源空间分布关联维数变化趋势进行对比发现,声发射关联维数能够很好地反映岩石内部损伤破坏的发展。在等压加卸载条件下,声发射源空间分布关联维数显著突增。随着加卸载循环应力的增加,关联维数总体呈下降趋势,在达到较高应力时,关联维数则在较小区间内波动或下降趋势变得极其缓慢。该特点可以作为矿山地压微震监测预警的参考依据。

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.