Granular columns have been used widely over the years to improve the load-bearing capacity of soft soils. Conventional granular columns are composed of stone aggregates, a non-renewable natural resource. Meanwhile, the global stockpile of plastic waste poses another serious threat to the sustainable existence of lives on our planet. This paper highlights the results of laboratory model tests performed on an embankment supported over a soft clay bed improved with granular columns (GC) and plastic granular columns (PGC). The model embankment was subjected to static and cyclic loading tests. The cyclic loading was applied in a 4-stage varying amplitude and single-stage loading. The experimental results show that the vertical load-bearing capacity of the soil bed improved by the granular column is increased by 71-135 % under static loading, respectively. The stresses induced in the column and soil bed were measured using earth and pore pressure transducers. Using GC and PGC, the cyclic load-induced settlements were reduced for both floating and end-bearing conditions compared to unreinforced soil. Using geosynthetic encasement further enhances the loading-bearing capacity, stress concentration ratio, and excess pore water pressure dissipation of the soil bed. The excess pore water pressure in unreinforced clay beds is reduced significantly. The stress concentration ratio (n) of the encased column improved bed is 1.51 and 1.50 times that of the non-encased end-bearing and floating columns. Geosynthetic encasement of GC and PGC significantly contributes to cyclic load-bearing capacity. The application of GC and PGC in soft clay improvement for the development of transportation routes and railway embankments is wellsuited based on the findings of this study.

The stone column encasement is a widespread ground improvement technique that effectively improves the engineering characteristics of weak and compressible soils with excessive settlement problems under vertical loadings. Despite the extensive use of stone columns, the settlement response of sandy soils reinforced with various geosynthetic encasement configurations under cyclic loading conditions remains unexplored. This study aimed to understand the settlement response of sandy soils reinforced with dual-layer geosynthetic-encased stone columns (DLGESCs), single-layer geosynthetic-encased stone columns (SLGESCs), and ordinary stone columns (OSCs) under cyclic loading conditions. The effects of cyclic loading amplitude, frequency, and geosynthetic encasement on settlement behavior were investigated using PLAXIS-3D (version 21) software with the hardening soil small constitutive model, and geosynthetic encasements with variable axial stiffness and tensile strength were studied. The study results indicated that higher cyclic loading amplitudes and frequencies increase the settlement of the stone column. DLGESC outperformed SLGESC with a 5.8%-11.2% settlement reduction, while SLGESC reduced settlement by 40.9%-47.8% compared to OSC. Geosynthetic GT3 (800 kN/m axial stiffness, 70 kN/m tensile strength) decreased settlement by 7.6%-13.6% compared to GT1. This research emphasizes ground improvement techniques and demonstrates the way DLGESC reduces settlement and improves structure stability on stone column-reinforced sandy soils. This study can help design resilient and stable foundations for pavements, railroad tracks, and offshore structures under cyclic vertical loading characteristics and suitable encasement configurations.

A series of undrained cyclic triaxial tests were carried out on loose sand specimens, including encased and non-encased granular columns, to evaluate the cyclic behavior and liquefaction resistance of the ground improved by granular columns. It was found that using geogrid encasements could effectively reduce cumulative settlements and mitigate the liquefaction potential when its tensile stiffness was high enough. Another finding was the inefficiency of flexible geosynthetic encasements to delay and mitigate the liquefaction in granular columns with the possibility of clogging. Findings indicated that the improvement of a loose ground with encased granular columns not only decreased the liquefaction-induced ground deformation but also significantly reduced the effect of earthquake magnitude on the ground deformation. It was also found that using the granular column and encasing it with a high-stiffness encasement not only slowed down the rate of ground softening during the cyclic loading experience but also decreased the dissipation of energy.

The efficiency of geosynthetics has been proven in stone column -reinforced foundations. In this paper, loading tests were conducted on three stone column -reinforced foundations, experiencing four freeze -thaw cycles. The effects of geosynthetic encasement and lateral reinforcement were investigated on the behavior of ordinary stone column (OSC) - reinforced and geosynthetic encased stone column (GESC) - reinforced foundation. The results showed that particles of OSCs spread into foundation soil during freezing and thawing, and top of OSCs were replaced by foundation soil. The temperature gradient along the depth in OSC-reinforced foundation was smaller than in GESC-reinforced foundations, resulting in a lower negative pore pressure at the beginning of freezing. However, it was found that geosynthetic encasement helped maintain the integrity of GESCs, and increased the stress concentration ratio (SCR) during thawing, which led to a lower excess pore pressure in GESC-reinforced foundations. The lateral reinforcement was also found to not only reduce the differential settlement between GESCs and soil during thawing, but also restrain the frost heave during freezing. The tensile membrane effect of lateral reinforcement redistributed the stress and the overburden pressure throughout the freeze -thaw process. More water moved upwards during freezing in the OSC-reinforced foundation, leading to a larger amount of frost heave. However, the moisture migration became complex in the OSC-reinforced foundation, as OSCs were damaged by freeze -thaw cycles.