## 6 Discussion
### Analysis of Disaster Patterns  
After the slope undergoes toppling deformation under gravity, a long period of geological evolution is required for instability, and different slope angles lead to differences in the final disaster patterns. Therefore, combined with the results of the centrifugal testing for the analysis of the characteristics and evolution of the toppling deformation of the models with different slope angles, we attempted to study and understand the disaster patterns of the toppling deformation from the perspective of the slope angle change (change of the free face condition of the slope).  
Figure 12: Developmental characteristics of the toppling bending zone, (**a**) 55\({}^{\circ}\) slope, (**b**) 65\({}^{\circ}\) slope, (**c**) 75\({}^{\circ}\) slope, (**d**) 3D schematics.  
The models with slope angles of 55\({}^{\circ}\) and 65\({}^{\circ}\) did not generate a secondary toppling-bending zone at any point during test. As the centrifugal acceleration increased and the time passed, the slope model sustained a longer time period and accumulated more failure energy for the final instability, and the result of this process reflected the overall deformation and failure. The disaster pattern under the effect of gravity may show the overall shear slip of the slope due to the penetration of the toppling-bending zone. This evolution and disaster pattern is shown in Figure 13.  
The model with a slope angle of 75\({}^{\circ}\) had a secondary toppling-bending zone inside the toppled rock layers, different from the other two slope models. The toppling of the slope was not an integral deformation failure. The rock mass above the secondary toppling-bending zone was closer to the slope surface, and thus, the rock mass broke and collapsed down to the slope foot during the formation process of the toppling-bending zone. The increase in the slope angle directly led to the generation of the multi-level toppling-bending zone of the toppling deformation rock mass, and the final result was that the toppling rock mass in the shallow surface of the slope collapsed. This destruction was also a kind of energy release and caused the slope deformation to temporarily converge. Meanwhile, the rock mass continued to generate toppling deformation under the effect of gravity, accumulating energy for the next collapse failure. This evolution and disaster pattern is shown in Figure 14.  
In conclusion, the variation in the free-face conditions of the slope could directly influence the degree of toppling deformation, the development characteristics of the toppling-bending zone and the final disaster pattern of the toppling deformation. Under identical conditions of slope height, dip angle of the rock stratum and thickness of the rock stratum, the lower the slope angle is, the more likely the toppling deformation will develop into an overall slide instability. The steeper the slope angle is, the more likely the toppled rock mass is to evolve into a collapse.  
Figure 14: “Toppling-collapse” disaster pattern. (**a**) settlement of slope bending of rock strata, (**b**) first-level toppling breaking zone, (**c**) second-level toppling breaking zone, (**d**) toppled rock mass.  
Figure 13: “Toppling–shear slide” disaster pattern.(**a**) settlement of slope bending of rock strata, (**b**) tension fracture of slope top, (**c**) penetrate of first-level toppling breaking zone, (**d**) toppled rock mass.