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.

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.

In this study, the seismic resilience of granular column-supported road embankments on liquefiable soils is examined to enhance the understanding and seismic design of resilient transportation infrastructure. A nonlinear dynamic analysis of embankments on liquefiable soils is performed, and the results are validated against centrifuge test data. In the assessment, a functional analysis framework encompassing fragility, vulnerability, and restoration functions is employed to evaluate the robustness and recovery of embankments. The resilience of embankments is quantified by the comprehensive life-cycle resilience index (R), which considers various factors, such as the embankment height, the liquefiable soil thickness, and the area replacement ratio (AR) of granular columns. A simplified design method is proposed that involves a model for rapidly assessing the resilience state of embankments under varying seismic intensities. The analysis highlights the essential role of granular columns in mitigating liquefaction-induced damage during seismic events, improving robustness, and recovering postearthquake functionality, and a practical and reliable tool is developed for assessing embankment resilience across diverse seismic scenarios.

This paper examines the impacts of deposition direction and density of granular soils on their large deformation behavior encapsulated by column collapse processes. We combine a critical state-based, anisotropic constitutive model for sand and material point method (MPM). The constitutive model includes state-and fabric-dependent dilatancy and hardening, thus accounting for the effects of density and deposition direction on the mechanical behavior of soils. The MPM model is first validated against experimental results. We then investigate the fundamental connections between local constitutive properties of soils (e.g., friction and dilation) and global column collapse response. Based on these correlations, this work further studies how material density and deposition direction influence collapse behavior, including run-out distance, residual height, and slope angle of the static region. Results indicate that run-out distance is relatively insensitive to initial soil density but can be significantly altered by the deposition direction of soils. Peak run-out distance is observed as the deposition direction is aligned with sliding band formed within the granular column. Moreover, a higher density or a smaller inclination of deposit direction leads to a greater residual height and a steeper slope of the static region. The mechanisms of above effects from soil properties perspectives are discussed.