Three-dimensional short-term stability analysis of clayey slopes stabilized with piles

Abstract

In this study, the short-term (undrained) behavior of pile- stabilized clayey slopes were investigated via three- dimensional (3D) finite element analysis. Deformations and stability conditions were investigated considering various soil strength parameters, slope geometries, pile material behavior, pile head conditions, and pile spacing-to-diameter ratios for slopes with and without surcharge loads. For the slopes without surcharge loads, the slopes were modeled as a representative slice model and the loaded slopes were modeled using the complete geometry of the problem to capture the 3D failure mechanism induced by the local surcharge loads. Initial case selection was performed using limit-equilibrium based slope stability analysis and based on the initial factor of safety values, slopes that were deemed feasible to be stabilized with piles were selected for the parametric study. Factor of safety values, internal pile forces, pile head displacements, and failure mechanisms were recorded and used to evaluate the performance of various pile-stabilized slope cases. The results indicate that using elasto-plastic pile models improves the accuracy of the analysis by better simulating pile behavior and coupled failure mechanisms, resulting in more reliable factor of safety values. The effectiveness of soil arching and pile stabilization decrease as the pile spacing-to-diameter ratios and slope heights increase. In cases of high and steep, natural slopes (slope height, H≥25m, slope angle, β≥56.3°), and high and gentle, loaded slopes (slope height, H≥15m, slope angle, β≤33.7°), marginal improvements were observed through stabilization by a single row of piles. For other slope geometries, pile stabilization performed reasonably well. When the factor of safety of a slope reduces below 1 due to surcharge loads, significant deformations occur, and stabilizing the slope with piles becomes an inefficient solution. In locally loaded slopes, central piles experience severe loading, leading to structural failure and subsequent slope failure. The employment of a pile cap to constrain pile head movements improves stability by ensuring an even load distribution among row of piles. The results highlighted the importance of 3D analysis when pile stabilized slopes are considered.