加勁砂樁穩固邊坡受滲流作用之流固耦合分析

Abstract

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This study presents a meticulous investigation of the performance of geosynthetic encased granular column (GEC) stabilized slopes under extreme seepage conditions through a series of finite element (FE) analyses, validated by one-gravity (1-g) model tests. The primary objective is to evaluate the effectiveness of GEC stabilized slopes as a remedial measure for natural slopes failing under severe seepage conditions. The research first employs a FE analysis of a natural slope, with a 50° slope angle and a total height of 6-meters, subjected to extreme seepage conditions, constructed atop an impermeable rock layer. This foundational scenario serves as a comparative basis against an OSC stabilized slope, GEC stabilized slope, a rigid pile stabilized slope, and a GEC stabilized slope with horizontal drainage conditions. The failure surface patterns are observed from the incremental shear strain (Δγs) and the results are scrutinized based on the progression of horizontal displacement (ux), top settlement (uz), dissipation of pore water pressure (PWP), and central line horizontal deflection of GEC. Numerical simulations of the aforementioned scenarios serve as the baseline, with their veracity validated through reduced-scale model experiments for final failure surface, phreatic surface progression, and the deformed surface profile of stabilized slope. The GEC-stabilized slope outperforms the limitations of rigid piles due to its vertical drainage capacity, which impedes the development of steady-state seepage conditions. Rigid piles, with their superior bending stiffness, restrict the movement of soil particles, inducing k0- conditions and a strong arching effect. Conversely, GECs, due to their lower bending stiffness, allow deformation, leading to ka-conditions. This mobilization of strain for GEC stabilized slopes results in a uniform distribution of stress in the horizontal direction (σxx) near the GEC. The inclusion of GECs effectively extends the failure timing of the slope in comparison to both the natural and rigid pile stabilized slopes. The research identifies two primary stabilizing mechanisms: arching effect and soil shear strain mobilization. The numerical results from the parametric study indicate that insertion of GECs increases the overall system stiffness, which does not necessarily enhance the slope stability. To secure adequate slope system stabilization against extreme seepage conditions, a proper quantification of the contribution of mechanical, hydraulic, and volume-controlling parameters is imperative. S/D ratio and diameter (D) are the most influential parameters where increment in stiffness of slope system caused the increment in horizontal deformation and failure timing. With properly installed horizontal drainage systems, GECs demonstrate their superiority as the most suitable solution. The study concludes with comprehensive design recommendations proposed for practical engineering applications.