Abstract:

The acoustic emission (AE) test of sandstone rock sample under uniaxial multi-step loading compression were carried out, and the AE signals were observed. The relationship curves of time-stress-AE parameters were established, and the characteristics and evolution laws of AE during the entire loading were analyzed accordingly. With the aim to reveal the critical slowing down phenomenon of rock deformation and failure, the autocorrelation coefficient and variance of AE parameters versus time were analyzed in-depth. The results demonstrate that: (1) the rock produces obvious acoustic emission during the multi-step loading process, and the acoustic emission ringing count becomes higher and higher as the loading level increases, and reaches the highest at the moment of failure of the rock sample; (2) the characteristics of acoustic emission RA(rise time/peak amplitude)-AF(average frequency) indicate that the tensile cracking prevails in the whole loading process, and the shear cracking gradually increases in the later stage of loading; (3) the variance and autocorrelation coefficient of parameters such as AE ringing count, rise time, peak frequency, and RA suddenly increase before the catastrophic failure of rock sample, which indicates that the obvious critical slowing phenomenon appears before rock failure; (4) the variance of peak frequency and RA can be used as key precursor indicators of rock damage and failure. In view of this, applying the analysis of the critical slowing phenomenon to brittle failure process of rock has very important scientific value and practical significance for in-depth understanding of the damage state and the precursors of catastrophic failure of rocks.

Key words: rock failure, acoustic emission, critical slowing down, precursory characteristics