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Stone columns technique is one of the ground improvement techniques for supporting geotechnical structures such as embankments and storage tanks. The use of conventional stone columns in very soft soils can be problematic because a significant proportion of their bearing capacity depends on the confinement provided by the surrounding soil. In order to overcome little confinement by soft soils, stone columns can be encased with a geotextile and this encasement can provide enough confinement to the column material that will lead to increased stiffness and bearing capacity of the column. This paper investigates the influence of the geotextile tensile strength, stiffness and of the column material on column performance as well as the role of the column in dissipating the excess pore water pressure generated in the surrounding soft soil. To accomplish that large-scale laboratory tests were carried out using a tank with dimensions 1.6m x 1.6m x 1.2m. The soft soil was instrumented with piezometers installed at different locations from the column. The results of the tests show that geotextile tensile stiffness is of major importance for the column bearing capacity and performance. It was also found that the column has an essential function in dissipating excess pore water pressures.