## 3 Results and Analysis
### Influence of Hydration on Mechanical Properties of Lamellar Shale  
Figure 6 shows the complete stress-strain curves of the lamellar shale samples for \(\beta\) = 30\({}^{\circ}\), under the confining pressure of 15 MPa, after different hydration times. It can be seen from Figure 6 that with the increasing hydration time, the elastic deformation  
Figure 4: Changes in compressive strength (deviatoric stress) of dry shale with various axial direction—lamina angles (\(\beta\)). Figure 5: Changes in elastic modulus (**a**) and Poisson’s ratio (**b**) of the dry shale samples with axial direction—lamina angles (\(\beta\)). stage gradually becomes shorter, and the compaction stage, plastic deformation stage and residual stress stage become more significant. For example, the strain increments of the dry sample, and the samples after 24-h hydration and 48-h hydration in the elastic deformation stage and plastic deformation stage are 0.58%, 0.49%, 0.42% and 0.12%, 0.22%, 0.55%, respectively. Compared with the dry sample, the axial strain increment in the elastic deformation stage of the sample after 48-h hydration reduces by 27.5%, and the axial strain increment in the plastic deformation stage increases by 358%. This indicates that with the increase in hydration time (water content), the lamellar shale gradually develops from elastic and brittle deformation to plastic deformation. This rule is similar to the result of bedding shale obtained in the literature [32], but the difference is that lamellar shale shows more significant change under the effect of hydration. This may be due to the fact that the inclusion of lamellar structures, which contain a lot of clay minerals, would have more significant swelling deformation after hydration compared with bedding shale [36]. Thus, the increase in rock particle spacing is more obvious, leading to the reduction in elastic brittleness and increase in plasticity and ductility [37]. Figure 7 shows the variation curves of the compressive strength (deviatoric stress) of lamellar shale with different hydration times under the confining pressure of 15 MPa. As shown in Figure 7, with the increase in hydration time, the compressive strength of lamellar shale gradually decreases, and the rate of decrease gradually reduces too. For example, for the sample with \(\beta=30^{\circ}\), the compressive strength of the sample after 24-h hydration decreases by 14.7% compared with that of the dry sample, and the compressive strength of the sample after 48-h hydration decreases by 8.6% compared with that of the sample after 24-h hydration. Comparing the compressive strength variation of the samples with different \(\beta\) affected by hydration, it is found that the compressive strength of the sample with \(\beta=30^{\circ}\) is more significantly affected by hydration than those of the samples with other \(\beta\). For example, after 48-h hydration, the compressive strength of the sample with \(\beta=30^{\circ}\) decreases by 22.0% compared with the dry sample, while the sample with \(\beta=0^{\circ}\) and \(90^{\circ}\) decreases by 15.0% and 20.2%, respectively. These findings are similar to those obtained for bedding shale [32], but compared with bedding shale, the compressive strength of lamellar shale with various \(\beta\) decreases more significantly. This may be due to the higher content of clay minerals in lamellar shale, which makes it can easier be hydrated, leading to a more obvious reduction in its mechanical properties. Especially for the sample with \(\beta=30^{\circ}\), its failure surface is closer to the lamellar plane, and the compressive strength would decrease more significantly. Figure 6: Complete stress–strain curve of the lamellar shale samples for \(\beta=30^{\circ}\) under confining pressure of 15 MPa, after different hydration times. Figure 8 shows the variation curves of the elastic modulus of lamellar shale with different hydration times under the confining pressure of 15 MPa.