Staged Damage Behavior and Acoustic Emission Characteristics of Rock-Like Materials under the Coupled Effects of Clay Mineral Content and Uniaxial Loading

Abstract

In this work, we investigated the effects of clay mineral content on the mechanical damage behavior and cracking mechanism of rock-like specimens with different bentonite (montmorillonite) contents by performing uniaxial compression tests. Based on the obtained stress–strain curves, the damage evolution stages and stress thresholds of the specimens were determined. The evolution of internal microcracks and microstructural characteristics of fracture surfaces was analyzed using acoustic emission (AE) technology and scanning electron microscopy. The results showed that the bentonite content remarkably affects the damage behavior and AE patterns of the specimens. With increasing bentonite content from 10% to 40%, the stress thresholds and elastic modulus decreased, the peak strain increased, and the cumulative AE ring count and energy decreased (following a negative power function), indicating that the AE activities were significantly weakened. Moreover, the transformation of AF-RA distribution pattern, the decrease in b-value and increase in proportion of the high peak frequency indicated that the dominant cracking mechanism has been changed from small-scale microtensile modes to large-scale microshear modes. The AE source location results reproduced the formation process of macrofractures. These differences in damage behaviors and AE characteristics caused by bentonite content are closely related to the microstructure features of the specimens. The critical slowing down phenomenon of aforementioned AE parameters can serve for predicting rock instability.