## 5 Conclusions  
In this paper, the anisotropy characteristics, fracture mode, and fracture mechanism of continental shale are analyzed based on the Brazilian tests with different layer orientations and the AE monitoring results. The main conclusions are as follows:  
(1) The lamination structure of continental shale is obvious and the cementation degree is weak. The mechanical parameters such as tensile strength and splitting modulus of matrix and lamination are weaker than those of marine shale. Layer orientations have a significant effect on the anisotropy of continental shale. The tensile strength of continental shale increases gradually with the increase of layer orientation, reaching a peak of 5.595 MPa at \(\theta=90^{\circ}\). The growth rate is slow at \(\theta=0^{\circ}\)-\(30^{\circ}\), the fastest at \(\theta=30^{\circ}\)-\(45^{\circ}\), and close to linear growth at \(\theta=45^{\circ}\)-\(90^{\circ}\). In addition, the splitting modulus at \(\theta=45^{\circ}\) is the smallest and the layer orientation effect is the most obvious. The splitting modulus at \(\theta=90^{\circ}\) is the largest, which is 4.02 times the minimum splitting modulus.  
(2) The layer orientation effect has a significant influence on the fracture mode of continental shale. The fracture modes of \(\theta=0^{\circ}\) and \(\theta=90^{\circ}\) are mainly the tensile failure of lamination and matrix, respectively. The cracks are in the form of straight through-center and crescent-shaped deviating-center. The crack morphology of \(\theta=30^{\circ}\)-\(60^{\circ}\) is straight and crescent-shaped, through-center or deviating-center compound modes. In particular, the crack morphology of \(\theta=60^{\circ}\) is the most complex, with secondary cracks connecting two adjacent main cracks, which indicates that the layer orientation of \(60^{\circ}\) seems to be more conducive to the formation of a fracture network. The mechanical analysis results show that the strength of the \(\theta=30^{\circ}\)-\(60^{\circ}\) samples are distributed within the envelope of tensile strength, and the fracture mode is a compound fracture of matrix and lamination.  
Figure 11: AE signal spatial distribution characteristics with different layer orientations.  
(3) AE monitoring results show that the AE location points are obviously deflected with the change of the layer orientations, and the spatial distribution of the AE location points are the same as the fracture path of the crack. AE signals gradually deviate from the center of the sample with the increase of the layer orientation, and the number of signals has an increasing trend. This is particularly prominent at \(\theta=60^{\circ}\), which further verifies that the crack morphology of \(\theta=60^{\circ}\) is the most complex.  
Conceptualization, X.W. and X.L.; methodology, X.W. and Q.G.; software, X.W.; validation, X.W., Q.G. and X.L.; formal analysis, X.W.; investigation, Q.G. and X.L.; resources, X.W.; data curation, X.W., Q.G. and X.L.; writing--original draft preparation, X.W.; writing--review and editing, X.W. and Q.G.; visualization, Q.G.; supervision, X.L.; project administration, X.W. and Q.G.; funding acquisition, X.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Doctoral Research Start-up Fund project of Liaoning University of Technology (grant number XB2022022), and the APC was funded by Liaoning University of Technology.  
Not applicable.  
For more information regarding data availability, please reach out to the corresponding author.  
The authors would like to thank the anonymous reviewers for the constructive comments, which helped improve this article. Special thanks to the support of the Doctoral Research Start-up Fund project of Liaoning University of Technology (grant number XB2022022).  
The authors declare no conflict of interest.