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.
Highlights
Granite is a type of felsic intrusive igneous rock, and widely distributed throughout the continental crust
The ultimate failure exhibits brittle behavior. (2) the number of acoustic emission (AE) hits and their energy can reach their individual peaks during crack closure, elastic and plastic deformation and failure
AE signals of weathered granite mainly result from crack growth and friction under uniaxial compression
Summary
Granite is a type of felsic intrusive igneous rock, and widely distributed throughout the continental crust. Mechanical properties of granitic rocks and associated fracture propagation are of importance for a variety of engineering applications, including tunneling, mining, quarrying operations, and slope stability. In severely weathered granite slopes, the threat of geological disasters remain serious.[1,2] For analyzing the stability of rock engineering, the microcrack identification is of fundamental importance, and the mechanical behavior and failure of rocks strongly depend on microcracks.[3,4,5,6] The acoustic emission (AE) is an elastic wave radiation as result of crack formation or plastic deformation, in particular, during the process of mechanical loading. It is necessary to monitor and characterize deformation, failure as well as AE activity of weathered granite. It is hopeful that the observed phenomena are potentially useful for detecting fractures during hydro-fracturing[20] or assessing slope instability.[21,22]
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