# Evolution Process of Toppling Deformations in Interbedded Anti-Inclined Rock Slopes
## 4 Discussion
### Evolution Process of the Interbedded Toppling
Due to the release of the restraint at the slope toe, further motion of the above rock columns occurs and progresses towards the rear part of the slope. The hard rock blocks slide along the existing tensile fractures and extrude the adjacent soft rock layers. Then several fracture zones gradually form by tracing the cross joints and tensile fractures in the multiple layers. Once the localized fracture zones gradually connect to form a connected failure surface, the overall movement of fragmented rock masses above this surface subsequently occurs, resulting in the ultimate failure of the slope. Since the fractured rock mass still has a certain layered structure, the movement is characterized by sliding, overturning, and downslope overlapping. The monitoring results of the average velocity of the slope can provide quantitative references for determining the evolutionary stages (Figure 9). Initially, the slope average velocity consistently decreases. The moment when the rate reaches its minimum value can be considered as the end of the initial shearing stage (70 s). Subsequently, as the velocity significantly increased, the slope is deemed to have entered the free rotation stage. At 240 s, the horizontal velocity of the slope decreases from 22.54 \(\times\) 10\({}^{-5}\) to 1.71 \(\times\) 10\({}^{-5}\) m/s, indicating that the slope evolution has entered the creep stage. At 475 s, the slope horizontal velocity surges from 1.61 \(\times\) 10\({}^{-5}\) to 5.97 \(\times\) 10\({}^{-5}\) m/s, indicating that the slope has entered the progressive failure stage. In addition, the magnitude of rotation in the rock columns can serve as an indicator to determine whether the slope has entered the creep stage. The dip angle of rock layers (\(\beta\)) in the creep stage exhibits a symmetrical structure across the THS (Figure 11c):  
\[\beta_{\text{min}}=\pi-2\alpha-\beta_{\text{max}}, \tag{7}\]  
where \(\beta_{\text{min}}\) is the dip angle of deflected rock layers that satisfy the symmetrical structure. \(\beta_{\text{max}}\) is the dip angle of undeflected rock layers. \(\alpha\) is the dip angle of the THS. When \(\beta<\beta_{\text{min}}\), the slope is likely to enter the progressive failure stage. The K73 rockslide is a typical example of the instability of anti-inclined rock slopes in the study area. [PERSON] et al. [12] conducted a study on the evolution process of this landslide through numerical simulation. The monitoring results of the joint damage factor indicate that the rock layer is initially subject to shear damage. Then the joint shear damage transforms into tensile damage as the rock columns rotate. Finally, the tensile damage of rock layers dissipates, and the slope achieves self-stabilization. The formation of the rockslide is triggered by the shear movement of the toe rock masses. The sliding surface develops along the cross joints and is located above the THS. It can be seen that the numerical simulation results of the K73 rockslide are closely aligned with the results of the base friction model test. In addition, the rockslide deposits are predominantly composed of nearly horizontal rock columns. Downslope overlapping of rock blocks can be observed at the slope toe. The failure characteristics of the physical model slope are generally consistent with the field investigation results of the K73 rockslide (Figure 14). Since the failure of anti-inclined rock slopes exhibits distinct stages, different mitigation measures should be applied based on the evolution stage of the slope. The initial rotation of rock columns is often accompanied by the gradual incision of rivers [10; 11; 37; 12]. Due to the extremely slow deformation rates of slopes compared to landslides and the eventual stabilization of deformations, monitoring should primarily guide the treatment of such slope deformations. Protective measures for the rock mass at the toe of the slope should be undertaken when necessary to prevent toppling deformations from developing into landslides [12].