Deformation and failure characteristics of weathered granite under uniaxial compression

Abstract

In this paper, we have examined the crack formation of weathered granite by monitoring acoustic emissions (AE) under uniaxial compression. Except for the uniaxial compressive strength (UCS), the thresholds have been determined for crack closure, crack initiation and crack damage, respectively. Moreover, the relationship has been preliminarily established between the AE energy and the rock damage variable. Compared to the deformation and failure characteristics of unweathered granite, the uniaxial compression strength and the elastic modulus of weathered granite are significantly decreased. Additionally, the acoustic emissions are consistently observed in the stage of original crack closure and loading-induced crack initiation followed by crack formation. The crack volumetric strain is an indicator for the crack closure and crack initiation, while the bulk volume strain is an indicator to the crack damage threshold. In elastic phase, AE signals are mainly caused by the micro-damage, while in plastic phase, AE signals are attributed to the plastic deformation. The AE cumulative parameter curves describe the damage evolution process, including the damage initiation and damage development for the weathered granite. The b-value of AE accompanying rock-fracturing is estimated, and oscillates between 1.0 and 1.7 on a long-term decreasing background, indicating a close correlation with the alternate occurrence of clustering. Of particular interest is that the two PZTs are appropriate for monitoring acoustic emissions under uniaxial compression.