## 3 Experimental Results
### Influence of Layer Orientation Effect on Crack Growth and Fracture Mode  
#### 3.3.1 Morphological Characterization of Crack  
Table 4 shows the fracture characteristics of continental shale at all different layer orientations under the Brazilian test.  
It can be seen from Table 4 that the fracture modes of samples with the same layer orientation are not the same. When \(\theta=0^{\circ}\), the three groups of tests showed different crack propagation characteristics: starting from multiple points at both ends, penetrating, and deflecting the center of the disc. The main crack morphology is a straight or crescent shape, accompanied by a secondary crack. Interestingly, almost all crack propagation directions are distributed along the lamination direction. It is worth mentioning that the crescent-shaped cracks in the third set of tests indicate that deflection occurred during the propagation stage and not through the center of the disc, which may be due to the layer orientation not being the ideal vertical alignment. When \(\theta=30^{\circ}\), the three groups of tests showed deviating-center propagation characteristics of single-point or double-point cracking. The crack morphology is a crescent shape or nearly straight, and the crack propagation path was simple without a visible secondary crack. At the initial stage of loading, the sample cracks along the lamination direction first and then deviates from the center of the disc to the two sides, but the deflection angle is small. When \(\theta=45^{\circ}\), the crack morphology is slightly more complex than that of when \(\theta=30^{\circ}\). The crack starts from both ends and propagates along the lamination plane or deviates from the center of the disc at a certain angle with the lamination. Obvious secondary cracks can be observed near the main crack, and the secondary cracks propagate at a certain angle with the lamination plane. When \(\theta=60^{\circ}\), the three groups of tests all showed the characteristics of straight or crescent-shaped deviating-center propagation with multiple cracks. At the same time, secondary cracks were generated in each test and connected to the two adjacent main cracks, which indicated that the secondary cracks' propagation is along the lamination plane direction. When \(\theta=90^{\circ}\), all samples show a single-crack morphology. The sample cracks from both ends, and the cracks were propagated in a folded or crescent shape, through-center, or slightly deviating-center. Due to the existence of primary microcracks in the lamination plane of the first and second samples, the microcracks were propagated along the microcrack direction (near the horizontal direction) during the crack propagation stage and then continue to be propagated along the vertical direction through the lamination plane until the whole disc  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multicolumn{5}{c}{**Layer Orientation \(\theta\) (\({}^{\circ}\))**} \\ \cline{2-6}  & \(0^{\circ}\) & \(30^{\circ}\) & \(45^{\circ}\) & \(60^{\circ}\) & \(90^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Typical fracture morphology of continental shale with different layer orientations under Brazilian test.  
was penetrated. The crack morphology is a crescent shape or a folded shape between the adjacent lamination plane, and there are occasional minor secondary cracks.