Critical slowing down phenomenon for predicting the failure of solid rocks and cement mortar materials: Insight from acoustic emission multiparameters

Abstract

Failure precursors with clear physicomechanical connotations are of great significance in predicting catastrophic instability in major constructions and rock engineering. Here, we conducted uniaxial compression tests on natural solid rocks and cement mortar materials and obtained their acoustic emission (AE) activity characteristics during the damage evolution to explore the feasibility of AE parameters in characterizing the failure precursory characteristics of building materials. Based on the critical slowing down theory, the curves of the variance and autocorrelation coefficient for AE multiparameters were analyzed. The results show that the sudden increase in the variance and autocorrelation coefficient of AE multiparameters can be used as primary and secondary criteria, respectively, for the identification of failure precursors. Their physicomechanical connotations were clear, characterizing the dominance of shear failure modes and the onset of accelerated fracture. The discriminability of failure precursors characterized by the critical slowing down of the AE energy rate, RA value, and RA/AF value was higher than that characterized by the critical slowing down of the cumulative AE ring count and peak frequency. Moreover, we found that the building materials with high brittleness, strength, and heterogeneity present a more significant critical slowing down phenomenon. In the view of early-warning time, the occurrence of precursory features identified by autocorrelation coefficient was earlier than the occurrence of precursory features identified by variance.