The type of improvement technique that will be applied to a soil beneath an embankment depends on the nature of the problematic soil existing at the site. Soft soils beneath embankments typically present high compressibilities and low shear strengths. In some cases, geosynthetic-encased stone columns (GECs) have shown advantages over other solutions to improve embankment behavior. The aim of this study is to investigate the performance of GECs by means of numerical and analytical methods. Finite Element Analyses were conducted to evaluate the behavior of ordinary and geosyntheticencased stone columns underneath an embankment. Parametric studies were then conducted to investigate the influence of geosynthetic stiffness, column spacing, friction angle of column material and Stress Concentration Ratio (SCR) on the performance of the columns. The results obtained have shown that there are several parameters that are of paramount importance in improving the performance of GECs, such as geosynthetics stiffness, column spacing and thickness of soft soil layer.

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The use of granular column is one of the ground improvement methods used for soft soils. This method improves the foundation soils mechanical properties by displacing the soft soil with the compacted granular columns. The columns have high permeability that can accelerate the excess pore water pressure produced in soft soils and increase the undrained shear strength. When it comes to very soft soils, the use of granular columns is not of interest since these soils present no significant confinement to the columns. Here comes the encased columns that receive the confinement from the encasement materials. In this study, the influence of the column installation method on the surrounding soil and the encasement effect on the granular column performance were investigated using numerical analyses and experimental tests. The results show that numerical simulations can reasonably predict the behavior of both the encased column and the surrounding soil.