# Evolution Process of Toppling Deformations in Interbedded Anti-Inclined Rock Slopes
These forces are generally applied by drawing a belt under the stationary model [27]. Therefore, the failure process of the slope model can be directly observed from above the model. Due to its cost-effectiveness, intuitive process and convenient operation, base friction model tests have been employed in the research of a range of rock slopes. For example, [PERSON] et al. [28] and [PERSON] and [PERSON] [29] utilized base friction model tests to explore the failure process of rock slopes with two dominant sets of joints, defining the conditions under which blocks undergo toppling or sliding. [PERSON] and [PERSON] [30] investigated the mechanisms of flexural toppling failures in the slope and underground opening through base friction model tests. [PERSON] et al. [31] conducted base friction model tests to explore the instability mode of the highway slope in Japan. These experiments indicated that the slope failure is defined by toppling, which was triggered by rainfall and subsequent degradation of rock mass strength. [PERSON] et al. [32] studied the evolution process of an anti-inclined rock slope with progressive river incision through use of physical models with base friction and use of numerical simulations. With the wide application of non-contact measurement technologies during the experiment process, the limitations of the base friction model tests in lacking quantitative monitoring data have been overcome, significantly enhancing the depth of exploration of experimental results [33; 34; 35]. In general, research on the mechanism of slope toppling deformations through physical model tests has yielded a rich harvest. However, current research efforts primarily focus on single lithology slopes. Indeed, the interbedded structure of soft and hard rock is commonly found in anti-inclined rock slopes [3; 36]. In Western China, approximately 63.3% of slope toppling deformations exhibit a structure characterized by alternating soft and hard rock layers [37]. Since rock slopes with interbedded strata can combine the features of both hard and soft rocks, the deformation and failure mechanisms of such slopes are more complex than those of single lithology slopes. Therefore, the evolution process of anti-inclined rock slopes with alternate soft and hard rock layers remains a topic in the field of engineering geology that urgently requires further in-depth research. Due to the rapid advancement of hydropower projects on rivers in Southwest China, a large number of toppling deformations have been identified along valleys, featuring alternating soft and hard rock layers. Some of these toppling deformations have evolved into landslides, such as the Mari landslide [38], Jiaxi landslide [39], Zhenggang landslide [11; 40], Gendakan landslide [10], and Mala landslide [41; 42]. Due to their unique interbedded anti-inclined slope structure, these landslides have complex failure mechanisms, large development scales and extremely long formation periods, which pose hazards to the construction of hydropower projects. The toppling evolution mechanism of interbedded anti-inclined rock slopes has become crucial for accurately assessing the stability of the slopes. Therefore, we utilized a typical anti-inclined rock slope with an interbedded structure as a prototype and conducted a base friction model test to study the slope evolutionary process. The DIC and PIV techniques were employed to capture the variations of slope deformation and velocity fields at different evolution stages. The aim of this study was to reveal the evolution process and instability mechanism of such slopes. The findings hold significant application and reference value for the evaluation of stability and treatment design of similar slope problems.