## 4 Numerical Model of Bedding Slope
### Analysis of Highway Slope Destabilization Process  
The zone maximum principal strains are shown in Figure 14. The sliding surfaces obtained from numerical simulation and actual investigation are relatively close to each other; especially in the front-edge part of the slope, they are basically the same, which reflects the reliability of the solution method based on the secondary development of FISH language considering the deterioration effect of rainwater on the geotechnical body and the buoyancy force. There are local differences between the calculated and actual sliding surface at the trailing edge of the slope, which is due to the fact that the shape of the sliding surface in the project is not only controlled by the rock layers, but also by the steeply dipping joints in the downslope direction. Combining numerical simulation and physical modeling experimental studies [29], the evolutionary process of the Zhuquedong highway landslide is visually reproduced. The slope destabilization has the following phases:  
Phase 1: Flexure and uplift state, as shown in Figure 15. Gravity-driven shear deformation and differential interlayer misalignment in the rear geotechnical body produces extrusion due to blockage of the front edge, and the combined action of extrusion and water pressure causes flexural and uplift deformation of the lower rock layers. As time  
Figure 14: Maximum principal strains and sliding surfaces of the highway slope. Figure 13: Factor of safety versus time curve for the natural slope. progresses, the trailing edge of the slope is tensile, and the geotechnical body at the slope surface begins to slide down in small quantities. Phase 2: Deformation exacerbation state, as shown in Figure 16. The tensile deformation at the trailing edge of the slope increases, and the middle and rear geotechnical body slips downward along the layer. The flexural and uplift deformation of the front edge of the slope is intensified and forms a fold-like bending pattern that produces localized crushing, mixing and densification of the rock at the end of the uplift. In addition, the extrusion and deformation of the rock layers toward the Danqing River in the riparian zone at the foot of the slope is intensified. Phase 3: Shear failure state, as shown in Figure 17. The upper-middle silty mudstone is shear deformed and continuously pushed forward along the soft interlayers, and deformation and damage continue to accumulate in the uplift and flexural fold structure. When shear failure occurs in this area, the geotechnical body slides rapidly along this through surface, and the slope undergoes an overall destabilization failure. The actual investigation found that before the occurrence of the landslide, there was a 2-3 m high water spray near the shear outlet at the foot of the slope, which illustrated the buoyant effect of water pressure on the uplift area. When the landslide occurred, water pressure in the fissures and pore spaces was released, driving the slide mass forward and into the Danqing River. After the end of the landslide, a linearly distributed water leakage phenomenon remained on the front edge. The geological survey results showed that the landslide bed outcropping was visible at the site, the surface abrasion was developed, and its direction was consistent with the dip direction of strata. The landslide mass was mainly composed of medium-thin laminated silty mudstone sandwiched by siltstone of the Lower Cretaceous Tonglanlong Formation, which basically maintained the laminae, and the rock at the front edge was bent and elevated, and these characteristics validate the reliability of the simulation experiments. Figure 16: Highway slope deformation exacerbation state. Figure 15: Highway slope flexure and uplift state. The destabilization processes and mechanisms of the Zhuquedong highway slope are as follows: the slope was subject to continuous heavy rainfall, and the ponding of water on the platform of the excavated section of the roadbed was more conducive to the infiltration of rainwater into the slope.