Characteristics of fractal and frequency bands at Kaiser signal of acoustic emission in granite under triaxial compression

Laboratory experiments on the characteristics of acoustic emission(AE)in high and low frequency channels of granite specimens under confining pressures from 1 to 30 MPa with cyclic loading and unloading were carried out.First, Kaiser points were determined by the guideline of stress-time-counts.Second, the characteristics of energy distribution for frequency bands at Kaiser and adjacent points were studied by means of the wavelet packet analysis technique.Third, the relevant fractal dimensions at Kaiser and adjacent points energy were obtained by using G-P algorithm.The results show that:(1) The main difference between characteristics of AE cumulative counts in two frequency channels is the magnitude of the numerical values.But the basic characteristics of AE counts and the locations of Kaiser points are similar in two frequency channels.(2) In the aspect of frequency bands at Kaiser points, the confining pressures have no obvious effect on the variation law of characteristic frequency bands at Kaiser points.The characteristic frequency bands at Kaiser points are 0-62.5 kHz and 187.5-250 kHz at the relative axial stress level less than 63.67% of peak stress, and 62.5-125 kHz as stress level exceeds 69.06% of peak stress.(3) The minimum values of relevant fractal dimensions are at Kaiser points.