Abstract: By the uniaxial compression tests of siltstone samples, frequency characteristics of acoustic emission (AE) signals in the failure process of siltstone rock were investigated based on HHT analysis. The results show that HHT is a kind of signal time-frequency analysis method based on principal component analysis, which can determine the major and minor components of the signals, and precisely describe the time-frequency characteristics of the signal with instantaneous frequency. The time-frequency distribution of AE signal of siltstone can be divided into three stages during rupture process: initial zone, wave zone, and quiet zone. Main frequencies of AE signals during rupture process of siltstone samples are associated with stress levels, that is, main frequency decreases with the increase of stress level be- fore siltstone failure. From the stable extension of crack to unstable extension, until the rock failure, high energy AE signals transfer from high frequency to low frequency, and its duration increases. Appropriate monitoring bands of AE signals during siltstone rupture process is 20-120 kHz.

Key words: siltstone, uniaxial compression, acoustic emission, frequency, HHT