Stone columns installed in extremely soft soils may significantly reduce the effectiveness of this treatment due to the insufficient lateral confinement provided by the soft soil. The encasement of columns with geotextiles is commonly used in these cases with satisfactory results thanks to the extra confinement provided by the geotextile to the column. The influence of the encasement on the behavior of stone columns is studied by means of drained triaxial tests performed on encased and non-encased samples of gravel. Two different densities of the gravel and two different geotextiles were tested. This study is focused on the increase in strength of encased samples compared with non-encased ones, the extra confining pressure provided by the geotextiles and the mobilized friction angle of the gravel. All of the results show the improvement achieved when the gravel is encased with the geotextiles. This effect is more significant at lower confining pressures. (C) 2016 Elsevier Ltd. All rights reserved.