## 7 Conclusions  
1. When the fault dislocation was slight, the deformation of the subgrade surface was diffuse, with the subgrade showing an S-shaped dislocation along the fault strike. Simultaneously, the soil on the surface of the subgrade and the foundation was thrust to both sides of the fault. This phenomenon adversely affects the sustainability of the subgrade. During a severe fault dislocation, numerous en echelon tension-shear cracks appeared on the surface of the subgrade and foundation, and compression crush zones emerged on the surface of the subgrade slope. Taking the intersection of the centerline of the subgrade top surface and the fault strike as the center, the tension-shear cracks and compression crush zones were roughly distributed in a centrosymmetric manner. Due to the presence of tension-shear cracks and the thrusting effect, the density of the subgrade significantly decreased, leading to cavities and subsidence on the subgrade's surface.
2. When the angle between the fault strike and the subgrade strike increased from 22.5\({}^{\circ}\) to 157.5\({}^{\circ}\), the range of uneven deformation of the subgrade induced by the fault dislocation decreased and then increased. When the angle was 90\({}^{\circ}\), the range of uneven deformation was the smallest. To minimize the impact of the fault dislocation on the smoothness of railway lines, it is recommended that the angle between the fault strike and the subgrade strike should be 90\({}^{\circ}\) or close to 90\({}^{\circ}\).
3. When the angle between the fault strike and the subgrade strike increased from 22.5\({}^{\circ}\) to 157.5\({}^{\circ}\), the angle between the main tension-shear crack on the top surface of the subgrade and the fault strike showed a trend of increasing and then decreasing. The maximum angle was 17.5\({}^{\circ}\) when the angle between the fault strike and the subgrade strike was 112.5\({}^{\circ}\). The minimum angle was 6.5\({}^{\circ}\) when the angle between the fault strike and the subgrade strike was 22.5\({}^{\circ}\). This conclusion can provide a reference for accurately determining the direction of the main tension-shear crack on the top surface of the subgrade.
4. When the angle between the fault strike and the subgrade strike increased from 22.5\({}^{\circ}\) to 157.5\({}^{\circ}\), the compressive stress along the subgrade strike decreased, while the tensile stress along the subgrade strike gradually increased. Tensile stress was the main cause of tension-shear cracks on the subgrade surface, while compressive stress was the main cause of the compression crush zone on the subgrade slope.  
(5) The tension-shear cracks formed in the subgrade and foundation were spiraled. With an increase in the depth of the subgrade and foundation, the angle between the cracks and the fault strike gradually decreased, converging on the strike-slip fault.  
Conceptualization, J.L., Y.Y. and J.Y.; methodology, J.L.; software, J.L.; validation, J.L., Y.Y., D.C., H.Y. and J.Y.; formal analysis, J.L.; investigation, J.L.; resources, J.L.; data curation, J.L.; writing--original draft preparation, J.L.; writing--review and editing, J.L.; visualization, J.L.; supervision, Y.Y., D.C., H.Y. and J.Y.; project administration, H.Y. and J.Y.; funding acquisition, Y.Y. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Fund of China Academy of Railway Sciences Group Co., Ltd. (No. 2021Y314).  
Data Availability Statement: Data is contained within the article.  
Authors [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] were employed by the company Railway Engineering Research Institute, China Academy of Railway Sciences Corporation Limited, Beijing, China. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.