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New objective method for the determination of crack initiation stress using acoustic emission data, A
Meyer, Bradley J.
Meyer, Bradley J.
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2018
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Abstract
Rockbursts, spalling, and overbreak are major concerns for the design and construction of tunnels, mines, and any underground excavations in high-stress environments. It is necessary to understand and properly characterize the crack initiation (CI) threshold of the surrounding rock, which has a significant influence on the occurrence and severity of these phenomena. Research has shown that examining pre-failure crack and damage accumulation observed during laboratory testing can provide a more comprehensive evaluation of a rock than peak strength values alone. One approach for damage characterization relies on the passive monitoring of acoustic emissions (AE) associated with microcrack formation during uniaxial compression testing. In this study, several AE-based methods for determining CI in various rock types have been evaluated for a diverse and expansive set of data. The current methods, when applied to large sets of data, have been shown to exhibit limited reliability and repeatability. In this study, previously acquired data was used to determine the strengths of each method and its ability to successfully determine the CI threshold value. For the cumulative acoustic emission hit (CAEH) method, the procedure was evaluated to determine areas of improvement. Three main points were identified to improve the approach: the appropriate level of smoothing to the raw data, initial point selection, and the efficacy of applying a translational shift. Based on these results and findings, a more universal and reliable analysis method has been proposed, the modified cumulative AE hit (MCAEH) method.
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