Coupling criteria and precursor identification characteristics of multi-band acoustic emission of gritstone fracture under uniaxial compression

In order to obtain the criteria and precursor characteristics of critical rock fracture, laboratory experiments on the characteristics of acoustic emission (AE) of gritstone specimens under uniaxial compression are carried out. The relationships between proportions of AE frequency bands and stresses in the process of rock failure are analyzed. The variation characteristics of proportions of two characteristic frequency bands with stresses are analyzed especially. The relevant fractal dimensions of AE amplitude at different stress levels are calculated and analyzed in the two frequency bands. A multi-band AE dominant frequency recognition criterion model is established based on the quantitative relationships between proportions of frequency bands and stresses. The results indicate that the distribution characteristics of the proportions of frequency bands can reflect the main failure stages of rock. In the process failure of rock, the proportions of AE lower frequency band signals (31.25~46.875 kHz) decrease firstly and then increase, and the proportions of AE higher frequency band signals (140.625~156.25 kHz) increase firstly and then decrease. The minimum value and the maximum value appear in the critical state of rupture in the lower and higher frequency bands. And the minimum values of the relevant fractal dimensions of AE amplitude appear in the critical state of rupture in the two frequency bands. Based on the coupling analysis of proportions of characteristic frequency bands and stresses, the accuracy for estimating and predicting the critical state of rock can be improved by using the variations of the proportions of characteristic frequency bands and the relevant fractal dimensions of AE amplitude.