The axial stress–strain relations of embedded granular columns encapsulated with flexible reinforcement were evaluated using an analytical procedure based on the cavity expansion method. This proposed method has firstly been verified through an experimental triaxial test on a reinforced sand specimen. A normalized relation was established between the volumetric change and the axial strain of soil to enable the analysis of granular material behavior under a continuous increase in lateral pressure. The analytical results show that the reinforced granular columns embedded in clay behave differently from granular columns subjected only to a constant confining pressure. It is found that reinforcing a column with a sleeve at the top portion will be adequate to prevent the column from bulging and also improve its load carrying capacity. The optimum skirting length that a sleeve can deter a granular column from bulging depends on the characteristics of the in situ soil and the stiffness and yield strength of the sleeve.