Abstract: A biaxial servo testing machine is used to simulate rockburst of a granite tunnel, and the acoustic emission (AE) system is applied to acquire the waveform signal. The dominant-frequency characteristics of AE signals from initiation to occurrence of rockburst are analyzed using the spectrum analysis theory. The results show that the dominant frequency interval of AE signal is from 0.4 to 110 kHz, and more than 99% of the dominant-frequency concentration is in the range of 35-65 kHz. The distribution of the dominant-frequency of the AE signal can be divided into three stages with the evolution of rockburst. In the early stage of rockburst initiation, the dominant frequency is in the range of 35-65 kHz and 15-25 kHz, a few of low frequency AE signal close to 0.4 kHz occurs, and high frequency around 110 kHz seldom appear. In the middle period of rockburst initiation, the low frequency around 0.4 kHz nearly disappears, but the high frequency around 110 kHz begins to appear. In the final stage of rockburst occurrence, the number of dominant-frequency in the range of 35-65 kHz plummets, the low frequency approximate to 0.4 kHz almost disappears, but the high frequency close to 110 kHz appears intensively. The study provides the fundamental understanding of optimizing the frequency band of AE monitoring, which has important theoretical significance with respect to monitoring and early warning of tunnel rockburst.

Key words: granite, tunnel rockburst, acoustic emission, dominant-frequency