Abstract: In order to explore the failure precursors of layered slate, five groups of slate with different bedding angles (β = 0º, 30º, 45º, 60ºand 90º) were carried out using uniaxial compression tests, and the failure mode, acoustic emission (AE) parameters and multifractal characteristics are analyzed. The relationship between multifractal spectrum width (Δα) and damage evolution was discussed, and the precursor and warning time of final failure based on multifractal were determined. The results indicate that: when the bedding angle β increases from 0º to 90º, the failure modes of slate firstly change from tension-splitting failure to splitting-shear, then to shear slip, and finally to tension-splitting. The sudden increase of AE counts and the continuous increase in low-frequency (LF) and high-amplitude (HA) signals can be identified as precursors for predicting the failure of rocks. The proportions of LF-HA signals in the crack coalescence stage firstly decrease and then increase with the increase of bedding angle, β. Furthermore, the time of the sudden increase in Δα occurs before the damage mutation, in details, with the increase of β, the early warning time of Δα increases first, then decreases and then increases again, and the early warning time of slate (β = 30º) is the longest.

Key words: slate, bedding angle, acoustic emission, multifractal, failure precursor