Abstract: To examine the failure characteristics and internal damage mechanism of the natural rock mass with cracks, this study conducts uniaxial compression tests on the specimens of gypsum material with the prefabricated cracks of oblique angles of 0?, 30?, 45?, 60? and 90? and with no pre-crack. Acoustic emission (AE) technology is used to measure sound signals and monitor full failure process and changes in sound waves. Spectral analysis of AE signals shows that the dominant frequencies detected during the specimen failure is lower than 500 kHz, while the noise is dominated by frequencies higher than this threshold. Hence, the noise can be removed reliably. An AE parameter, namely hits per second (HPS), is used to evaluate AE intensity. The failure modes of the specimens are divided into three categories: crushing (0?), compression-shear (30?, 45? and 60?), and splitting (90? and no pre-crack). Multiple regression analysis is used to improve the AE time-difference-of-arrivals (TDOA) location algorithm, achieving satisfactory results in locating internal failure points.

Key words: acoustic emission, prefabricated crack, wave velocity, plane location, spectrum analysis, uniaxial compression