Colluvial landslides are mainly composed of soil-rock mixtures with complex composition and structure, resulting in large uncertainties in mechanical properties. This leads to difficulties in designing stabilizing piles for colluvial landslides. In this study, we derive a predictive model for the ultimate lateral force of stabilizing piles in soil-rock mixtures, and use it to evaluate the factor of safety of a pile- stabilized colluvial landslide. Subsequently, robust geotechnical design is employed to optimize the design of the stabilizing piles. The design robustness is measured by the variation of failure probability, an approach which can overcome difficulties in characterizing uncertainties in soil-rock mixture mechanical properties. Accordingly, we propose a robust design procedure for stabilizing piles for colluvial landslides. The design method and procedure are illustrated using a real colluvial landslide case study, out of which the most preferred design considering the safety, cost, and design robustness is obtained. Moreover, the influences of rock blocks and safety requirements on the optimal designs are discussed. Our results show that the angle of repose of the rock blocks and the volumetric block proportion determine whether the mechanical parameters of the soil matrix can be used to effectively design the stabilizing pile. It is also found that a higher safety requirement can improve the design robustness, but at higher cost. The advantages of the proposed method are illustrated by a comparison with the traditional reliability-based design method. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

With the construction of the Three Gorges Reservoir dam, frequent reservoir landslide events have been recorded. In recent years, multi-row stabilizing piles (MRSPs) have been used to stabilize massive reservoir landslides in China. In this study, two centrifuge model tests were carried out to study the unreinforced and MRSP-reinforced slopes subjected to reservoir water level (RWL) operation, using the Taping landslide as a prototype. The results indicate that the RWL rising can provide lateral support within the submerged zone and then produce the inward seepage force, eventually strengthening the slope stability. However, a rapid RWL drawdown may induce outward seepage forces and a sudden debuttressing effect, consequently reducing the effective soil normal stress and triggering partial pre- failure within the RWL fluctuation zone. Furthermore, partial deformation and subsequent soil structure damage generate excess pore water pressures, ultimately leading to the overall failure of the reservoir landslide. This study also reveals that a rapid increase in the downslope driving force due to RWL drawdown significantly intensifies the lateral earth pressures exerted on the MRSPs. Conversely, the MRSPs possess a considerable reinforcement effect on the reservoir landslide, transforming the overall failure into a partial deformation and failure situated above and in front of the MRSPs. The mechanical transfer behavior observed in the MRSPs demonstrates a progressive alteration in relation to RWL fluctuations. As the RWL rises, the mechanical states among MRSPs exhibit a growing imbalance. The shear force transfer factor (i.e. the ratio of shear forces on pile of the nth row to that of the first row) increases significantly with the RWL drawdown. This indicates that the mechanical states among MRSPs tend toward an enhanced equilibrium. The insights gained from this study contribute to a more comprehensive understanding of the failure mechanisms of reservoir landslides and the mechanical behavior of MRSPs in reservoir banks. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).