Full Life Cycle Evaluation of Stability Pile in High Slope with Multi-Layer Weak Interlayers

High slopes with multi-layer weak interlayers are a type of special slope that tends to fail due to the unfavorable mechanical properties of interlayers. In this study, the influence of the position, length, diameter, and ratio of on-center spacing to the pile diameter on the stability of such slopes is investigated using the three-dimensional strength reduction elastoplastic finite element method. Based on a high slope with multi-layer weak interlayers, two models were created, and three states (an initial state, a state with a safety factor of 1.35, and a limit equilibrium state) were considered. The pile can improve slope stability when the it is located at the lower to lower-middle part of a high slope. The resistance effect no longer has a strengthening property if it exceeds a critical pile length (28 m and 30 m in the two models); 30 m was found to be the optimal pile length for the high slope. As the diameter increased, the safety factor increased from 1.38 (1.37) to 1.41 (1.40) in Model 1 (or in Model 2), while the maximum compressive stress, the maximum shear stress of the pile, and the maximum displacement of the pile head decreased in the two models from 20.84 (81.24) MPa to 16.15 (18.8) MPa, 11.19 (42.02) MPa to 7.77 (10.43) MPa, and 714.1 (4585.00) mm to 396.3 (1272.00) mm, respectively. The pile diameter should be >1.4 m in such cases. When stress and displacement increased, the arching effect and the pile group effect weakened, and the safety factor decreased as the ratio of on-center spacing to diameter increased. The ratio should be <3 to ensure slope ability.