# Evolution Process of Toppling Deformations in Interbedded Anti-Inclined Rock Slopes
## 4 Discussion
### Evolution Process of the Interbedded Toppling  
According to the physical model experiments, the instability of the anti-inclined rock slopes mainly entails early large-scale toppling deformation and later rapid sliding failure. The development of toppling deformation depends on the level of the constraint offered by the materials surrounding the rock column, while the progression to ultimate failure relies on the formation of potential failure surfaces within the deforming body. Overall, the evolution of an interbedded anti-inclined rock slope undergoes the following five stages:  
The steeply dipping rock columns overcome the frictional resistance on the side faces from adjacent columns and facilitate shear slip between the parallel rock layers. Due to the tight contact between adjacent rock columns, the deformation rate of the slope is slow. Figure 12: Failure features of interbedded toppling events: (**a**) A typical toppling-induced fracture zone within a slope. The white dotted lines denote rock layers. The red dotted lines denote the boundary of the toppling fracture zone; (**b**) The K73 rockslide, a typical landslide developed from a deep-seated toppling deformation, and the failure surface was formed based on fracture zones above the THS. The red dotted line denotes the boundary of the K73 rockslide. Figure 13: Evolution process of toppling in interbedded anti-inclined rock slopes: (**a**) Initial shearing stage; (**b**,**c**) Free rotation stage; (**d**) Creep stage; (**e**,**f**) Progressive failure stage. The blue arrows denote the direction of the interlayer shear dislocation. The straight red arrows denote the direction of the tensile stress within the rock column. The curved red arrows denote the movement trend of the rock column. The yellow zone denotes the landslide deposit. (2) Free rotation stage (Figure 13b,c)  
As the degree of toppling deformation increases, tensile damage along rock layers rapidly develops and progresses to the lower and deeper parts of the slope. As frictional resistance on the column faces significantly decreases, rock columns undergo accelerated rotation under the effect of gravity. In this stage, rock columns exhibit significant toppling deformation toward the free surface. Soft rock columns undergo ductile bending deformation. Hard rock blocks overturn forward and create numerous tensile fractures based on the cross joints that are present near the slope surface. The formation of the tensile fracture between the adjacent rock layers depends on the differential deformation of soft and hard rocks. On the other hand, the interlayer tensile fractures are likely to be formed by the effective contractional strain which develops parallel to the THS during column rotation [47; 48]. In the later period of this stage, tensile fractures perpendicular to the rock layer occur due to sufficient bending deformation. (3) Creep stage (Figure 13d)  
As rock columns rotate further, the tensile fracture between the adjacent columns gradually disappear, and the side faces of columns are returned into contact. At this point, the further motion of the rock columns is resisted by the increasing interlayer shear forces, and the slope motion tends to be self-stabilized. According to the results of physical model experiments, the deformation rate decreases to approximately 0, and the displacement of the slope essentially ceases to progress. The numerical simulation results from [PERSON] et al. [12] also indicate that the toppling deformation in anti-inclined slate slopes experiences a significant creep stage after initial rotation. Furthermore, such phenomena have been widely observed in the field as well [7; 46; 47; 48]. Based on the strain compatibility theory, the creep stage of toppling can be identified by a mirror image condition of rock layers across the THS [47]. (4) Progressive failure stage (Figure 13e,f)  
Further motion beyond the self-stabilization state is generally induced by the shear slide of the blocks at the slope toe.