# Full Life Cycle Evaluation of Stability Pile in High Slope with Multi-Layer Weak Interlayers
## 1 Introduction  
Weak layers are widely distributed in high rocky slopes; they strongly affect the stability, deformation, and failure of rock masses [1, 2]. Because these layers have relatively unfavorable physical and mechanical properties [2, 3, 4], they are of great importance in the study of large landslides, such as the Huangtopo landslide, the Qianjiang lang landslide, and the Anleisi landslide [5, 6, 7, 8]. Researchers have made efforts to explore and investigate the failure mechanisms of slopes with weak interlayers, as can be seen in the literature. [PERSON] [9] and [PERSON] [10] analyzed the stability of steep rock slopes. Based on geological and laboratory determinations, [PERSON] [11] back-analyzed the failure of clay-filled bedding planes in limestone. [PERSON] and [PERSON] [1] evaluated the mechanical properties of a weak intercalated layer of a slope by in situ large-scale shear tests, finding that the plastic failure of slopes is controlled by the weak layer. The evolution from a soft stratum to a weak interlayer provides the possibility of kinematic release, which was one of the mechanisms of the deformation of the Mayampo rock slope [4]. [PERSON] et al. [12] revealed that the strength deterioration of interlayers induced by water further increases the possibility of landslides. In addition, excavation also compromises the integrity of rock masses, where multi-layer weak interlayers are particularly significant [13]. Therefore, supporting measures are important to increase slope stability and avoid failures in high slopes with weak interlayers, especially those with multi-layer weak interlayers. Stability piles are a type of supporting measure to improve the stability of slopes; they have been quite widely implemented. The position, length, diameter, and other factors of piles affect their supporting effect and, therefore, the stability of the slope [14]. Because of differences among methods, the optimal pile position may range from the toe to the top of the slope [15; 16; 17]. The position also depends on the type of rock and soil mass: middle for a sandy slope, and middle-lower for a soft soil slope [18]. The lengthening of piles promotes slope stability [19]. Increases in the safety factor (\(F\)) relative to increases in pile diameter are limited in silty sand slopes [20]. The arch effect weakens and \(F\) decreases with increases in the ratio of on-center spacing to pile diameter [21]. [PERSON] et al. [22] proposed that piles influence horizontal displacement and that a pile with a length of 15 m, a diameter of 1.5 m, and a spacing of 2.5 m can ensure the stability of a high embankment. However, the slopes described in the above studies were all single-stage slopes without weak interlayers, which means that the supporting effect of pile with multi-layer, weak interlayers should be evaluated further. Methods such as the limit equilibrium method [14; 23; 24], the limit analysis method [14; 15; 16], the shear strength reduction finite element method [17; 25; 26], and the upper-bound theorem of limit analysis [27] are widely used in pile design. These methods consider the initial state, the equilibrium state, the critical state, or the limit equilibrium state [15; 25; 27; 28; 29; 30; 31]. However, interactions between rock, soil mass, and the pile change in real time, which means that the pile may experience two or even more states. Therefore, it is necessary to evaluate the effect of piles over their full life cycle. To more closely examine the phenomena described above, a high, multilevel slope located at the southern edge of the Yuxi Basin in Yunnan Province, China (24\({}^{\circ}\)14\({}^{\prime}\)48\({}^{\prime\prime}\) N, 102\({}^{\circ}\)33\({}^{\prime}\)4\({}^{\prime\prime}\) E) (Figure 1), with multi-layer weak interlayers is taken as a typical case.