Abstract: In the aim of obtaining the criteria and precursor characteristics of critical rock fracture, uniaxial compression acoustic emission experiment was performed on granite to acquire the time and frequency domain signal information of acoustic emission during the whole process of rock deformation and rupture. According to the spectrum analysis theory, the dominant-frequency value of the waveform signal was extracted, and the parameters of time and frequency domain are combined to analyze the variation features and the identification information of rupture precursors. Results unveiled that the acoustic emission event rate alternated between high and low values before the high-stress stage, and between high and medium values after the high-stress stage; the cumulative number of events climbed rapidly with increasing load, but suddenly tended to be gentle at very high stresses. The energy rate and cumulative energy can be divided into two active periods and one slowly releasing period with the loading process. The dominant-frequency can be divided into five frequency bands of 1^#-5^#, therein the 2^# frequency band corresponded to the main rupture mode of rock’s rupture process, the 3^#, 4^#, 5^# frequency bands belonged to the high frequency band, and the 1^# frequency band belongs to the low frequency band, with the high and low frequency bands respectively corresponding to the initiation of microcracks and the formation of large cracks by microcrack closure. The parameters of time-frequency domain in the acoustic emission are of good precursor recognition characteristics. The time response sequence of rupture precursor follows the order of dominant-frequency, event rate, energy rate and cumulative energy, and then cumulative number of events.

Key words: rock mechanics, acoustic emission, time and frequency domain, uniaxial compression test, precursor characteristics