Post-grouting pile technology has gained extensive application in collapsible loess regions through the injection of slurry to compress and consolidate the soil at the pile base, thereby forming an enlarged base that enhances the foundation's bearing capacity and reduces settlement. Despite the prevalent unsaturated state of loess in most scenarios, the conventional design methodologies for piles in collapsible loess predominantly rely on saturated soil mechanics principles. The infiltration of water can significantly deteriorate the mechanical properties of loess due to the reduction in matric suction and the occurrence of collapsible deformation, leading to a substantial degradation in the bearing behavior of piles. To explore the variations in load transfer mechanisms of post-grouting piles in collapsible loess under conditions of intense precipitation, a comprehensive large-scale model test was conducted. The findings revealed that the post-grouting technique effectively mitigates the adverse effects of negative pile shaft friction in saturated zones on the pile's bearing behavior. Furthermore, the failure criteria for piles may shift from the shear failure of the base soil to excessive pile settlement. By incorporating principles of unsaturated soil mechanics, modified load transfer curves were developed to describe the mobilization of both pile shaft friction and base resistance. These curves facilitate the extension of the traditional load transfer method to post-grouting piles in collapsible soils under extreme weather conditions. The proposed revised load transfer method is characterized by its simplicity, requiring only a few soil indices and mechanical properties, making it highly applicable in engineering practice.

Pile-supported embankments are one of the most commonly used techniques for ground improvement in soft soil areas. Existing studies have mainly focused on embankments supported by end-bearing piles under static loading, with limited research on floating pile-supported embankments under cyclic traffic loading. In this study, model tests for unreinforced floating, unreinforced end-bearing, geosynthetic reinforced floating, and geosynthetic reinforced end-bearing pile-supported embankments were conducted. Cyclic traffic loading was simulated using a three-stage semi-sinusoidal cyclic loading. Comparative analyses and discussions are performed under floating and end-bearing conditions to investigate the influence of floating piles on the soil arching evolution and membrane effect under cyclic loading. The results indicate that floating piles result in earlier stabilization of surface settlement. There is less arching and membrane effect induced by floating piles, and the arching does not continue to degrade under cyclic loading. Less membrane effect in floating pile-supported embankments results in less geosynthetic and pile strain. The degree of membrane effect in floating pile-supported embankment largely depends on the pile-end condition.

This paper presents a discrete element method (DEM) investigation into the load transfer mechanisms and failure surfaces of geosynthetics reinforced soil (GRS) bridge abutments. A local strain-dependent reinforcement contact model is developed to accurately simulate the nonlinear tensile behavior of reinforcement. The study analyzes both the macroscopic deformation response and the microscopic fabric evolution of backfill soil under bridge load. The findings reveal that as the bridge load increases, the micro-bearing structure of the soil within the potential failure surface evolves through progressive loss of effective contacts, particle rotation, and fabric reorganization. These micromechanical phenomena underlie the development of shear bands and the global failure mechanism of GRS abutments. Furthermore, a parametric analysis is conducted to evaluate the effects of reinforcement stiffness, reinforcement vertical spacing, and backfill soil friction angle on failure surfaces of GRS abutments. The results demonstrate that higher reinforcement stiffness constrains failure surface development, while wider reinforcement spacing and lower soil friction angles lead to deeper and more pronounced failure surfaces. Overall, the study highlights the critical role of reinforcement-soil interactions and micromechanical processes in determining the deformation and failure surfaces of GRS bridge abutments.

This paper presents a numerical study to investigate the load transfer mechanism of a geosynthetic encased stone column (GESC) under embankment loading. The soils were modeled with a nonlinear elasto-plastic constitutive model incorporating a hyperbolic stress-strain relationship and the Mohr-Coulomb failure criterion. The geosynthetic encasement was modeled using a linearly elastic embedded liner element. Two interfaces were used to simulate the interaction between the geosynthetic encasement and the soils on either side. The validation of the numerical model was conducted using test data from vertical loading tests of the individual GESC installed in loose sand, including applied vertical stress-settlement curves and the circumferential strains profiles. Then, the influences of different design parameters on the load transfer mechanism of the GESC unit cell were investigated through a parametric study. Results indicate that the development of stress concentration ratio depends on the mobilization of tensile strains. The circumferential strains are significantly larger than the longitudinal strains, indicating that the circumferential tensile effect is dominant under embankment loading. The load transfer effect was gradually enhanced with increasing tensile strains. Increasing the geosynthetic encasement stiffness can be considered as an alternative to increasing the column infill friction angle in improving the load transfer effect.

Pile-supported embankments are commonly employed for highways in soft soil areas. Extensive studies have been conducted on high embankments under static loading. However, low embankments with lower costs and carbon footprint have not yet been thoroughly studied. This study aims to investigate the performance of pilesupported low embankments under cyclic traffic loading by carrying out two large-scale model tests. The soft soil was constructed using Kaolin clay, and the cyclic traffic loading was simulated using a localized semisinusoidal function. The effect of geosynthetic reinforcement on the load transfer mechanism of pilesupported low embankments was investigated by comparing the measured data from unreinforced and reinforced cases. Test results show that geosynthetic reinforcement reduces settlement and leads to faster stabilization of settlement in low embankments. Pile-supported low embankments experience a rapid decrease followed by a stabilization in pile efficacy with increased cyclic loading, and geosynthetic reinforcement increase the pile efficacy and facilitate quicker stabilization. Geosynthetic reinforcement enhances the transfer of static and dynamic stresses to piles, resulting in less stress degradation under cyclic loading. Based on experimental results, pile-supported embankments should account for the adverse effects of cyclic loading, even if they are classified as high embankments according to existing analytical models.