## 4 Conclusions  
Using the lamellar shale in the continental stratum of the southern Ordos Basin, the mechanical properties and corresponding mechanisms of lamellar shale were studied by compression tests and CT scanning tests, considering the effect of lamellar structure and hydration. Based on the results, the following conclusions can be drawn. First, under the same conditions, the compressive strength and elastic modulus of bedding shale are both greater than those of lamellar shale, and the anisotropic magnitude of lamellar shale is greater than that of bedding shale. Second, the complete stress-strain curve of lamellar shale has a longer elastic deformation stage, but compared with bedding shale, its compaction stage, plastic deformation stage and residual strain stage are more significant. While the axial direction-lamina angle (\(\beta\)) of sample is closer to \(30^{\circ}\), the compaction stage and plastic deformation of the sample would be more obvious, and the elastic deformation stage would be shorter. Third, with the increase in \(\beta\) from \(0^{\circ}\) to \(90^{\circ}\), the compressive strength of lamellar shale decreases when \(\beta<30^{\circ}\) and then increases, showing a \"U\"-shaped variation relationship; the elastic modulus of lamellar shale decreases greatly when \(\beta<30^{\circ}\) and then tends to flatten; Poisson's ratio increases when \(\beta<30^{\circ}\) and then decreases rapidly. With the increase in confining pressure, the anisotropy magnitude of lamellar shale decreases gradually. Fourth, with the increase in hydration time, the elastic deformation stage of lamellar shale becomes shorter, and the compaction stage, plastic deformation stage and residual stress stage become more significant. The compressive strength and elastic modulus of lamellar shale gradually decrease, and the rate of decrease reduces too. Under the influence of hydration, lamellar shale will develop from elastic-brittle deformation to plastic deformation. Moreover, when \(\beta\) is closer to \(30^{\circ}\), the compressive strength and elastic modulus of lamellar shale decreases more significantly, and the development towards plastic deformation becomes more obvious. Fifth, the failure of lamellar shale is significantly affected by the clay minerals lamina. Hydration causes the expansion of clay mineral lamina to produce tensile fractures. In triaxial compression tests under high or low confining pressures, the failure occurs along the lamina direction, making the plasticity of lamellar shale become stronger and the mechanical properties decrease significantly. Finally, the mechanical properties of lamellar shale after hydration, as mentioned above, can provide guidance for the study of borehole instability mechanisms and borehole stability analysis of lamellar shale formation during drilling operations using water-based drilling fluid. Conceptualization, Q.Z. ; methodology, Q.Z. and L.H. ; validation, F.Z. ; formal analysis, Y.F. ; investigation, L.W., P.Z. and S.Y. ; resources, X.F. ; data curation, L.W. ; Writing-original draft, L.W. ; writing--review and editing, Q.Z., P.Z. and B.Y. ; funding acquisition, X.F. ; supervision, X.F. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (Grant Nos. 42172313 and 51774246) and the financial support from the Key Laboratory of In-situ Proper-ty-improving Mining of Ministry of Education, Taiyuan University of Technology (Grant No. KLIPM-2019-03). Not applicable. The data presented in this study are openly available in [Mendeley Data] at [[[https://doi.org/10.17632/shmkw9](https://doi.org/10.17632/shmkw9) kf2g.1]([https://doi.org/10.17632/shmkw9](https://doi.org/10.17632/shmkw9) kf2g.1)]. The financial support from the National Natural Science Foundation of China (Grant No.