Abstract
In this paper, the potential of 3D acoustic emission (AE) tomography technique in demonstrating fracture development and delineating stress conditions was examined. Brazilian tests and uniaxial compression tests were monitored by 3D AE tomography. AE counts, AE source locations and 3D tomographic images of locally varying velocity distributions were analyzed along with stress and strain measurements. Experimental results revealed two distinct failure processes between Brazilian tests and uniaxial compression tests indicated by differences in AE counts, source locations and the temporal variation of velocity. Furthermore, the development of micro-cracks showed by the results correlated well with theoretical analysis and experimental observations. Additionally, stress patterns, failure modes and final failure planes were indicated by AE locations and velocity tomography. Three-dimensional velocity tomographic images indicated the anisotropy of samples caused by stresses as well. These results confirm the usefulness of AE tomography as a method to monitor stress induced failure and the potential of AE tomography for delineating stress conditions and predicting rock failure.
Highlights
Understanding fracture development such as crack closure, crack initiation, crack growth and crack coalescence in stressed rock allows us to have a better understanding of rock behavior
We demonstrate that the P-wave velocity varies during either uniaxial compression test or Brazilian test because of noticeable changes in micro-crack densities during tests
The above conclusions in this study suggest the usefulness of AE tomography technique as a method for monitoring fracture development induced by loading
Summary
Understanding fracture development such as crack closure, crack initiation, crack growth and crack coalescence in stressed rock allows us to have a better understanding of rock behavior. This information will eventually benefit geotechnical engineering projects. The crack initiation observed in laboratory uniaxial tests provides a lower bound limit for in-situ spalling strength in hard brittle rocks around underground excavations (e.g., Diederichs, 2007; Andersson et al, 2009; Martin and Christiansson, 2009; Rojat et al, 2008) and it may be used as a lower bound estimate for the long-term strength threshold of crystalline rocks (Damjanac and Fairhurst, 2010). The imaging of cracks by optical methods is only limited to the surface of specimen while
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