The bedding orientation influences the failure pattern and brittleness of shale. Clarifying the relation between acoustic emission and the effects of bedding orientation on the failure behaviors of shale is important to understand the mechanism of the formation of fracture networks. In this study, we analyzed the failure patterns and crack complexity of the shale specimens with various bedding orientations under uniaxial compression using X-ray computed tomography. We proposed an improved criterion based on the acoustic emission waveform parameters to identify the mechanism of the acoustic emission events and showed that the failure mechanism changed from tension to shear during the failure process of each specimen because the shear cracks link independent tensile cracks to form macrofractures in the later loading stage. The proportion of shear-mode events in the specimens declined when the bedding orientation angle increased from 0° to 90°, whereas that of the tensile-mode events exhibited an opposite trend; these changes were consistent with the observation results of X-ray images, indicating the transition of the dominant failure mechanisms with the bedding orientation. The large b value of the acoustic emission events corresponded to a complex crack distribution; thus, this b value may be useful to evaluate the brittleness of shale. These results denote the relation between the mechanisms of the failure patterns in shale and the acoustic emission activity and improve our recognition to the fracture network characteristics.
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We would like to thank Dr. Li Guoliang and Ms Niu Suyun (Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences) for assistance in CT imaging and dataset processing, Miss Zhang Ke (Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences) for assisting with the calculation of the fractal dimension. We would also like to thank Enago for reviewing the language of our manuscript.
This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences [Grant Numbers XDA14050101, XDA14020401 and XDB10030302], the National Key Research and Develop Program of China [Grant Number 2019YFA0708301], the China Postdoctoral Science Foundation [Grant Number 2018M640181], and the National Natural Science Foundation of China [Grant Number 41602330].
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Chen, H., Di, Q., Zhang, W. et al. Effects of bedding orientation on the failure pattern and acoustic emission activity of shale under uniaxial compression. Geomech. Geophys. Geo-energ. Geo-resour. 7, 20 (2021). https://doi.org/10.1007/s40948-021-00216-x
- Bedding orientation
- Acoustic emission
- Computed tomography
- Failure pattern