Abstract: The upper-geosynthetic-encased stone column (UGESC) is widely used in engineering practice as a composite foundation. Its failure modes are analyzed herein. Two models are established for the swelling failure mode of UGESC based on the Meyerhof approach and the Terzaghi approach for calculating the bearing capacity of deep foundations by introducing the block limit equilibrium method and considering the effect of self-weight of soils and surrounding skin friction of the encased segment. The stochastic optimization algorithm is employed to search for the critical slip surface, and the corresponding ultimate bearing capacity can be obtained by solving the established models. The comparative analysis of the test results and those from other approaches demonstrates that this novel computing method coincides more with the engineering practice. With respect to the bearing capacity, the optimal encased depth of UGESC is approximately four times the diameter of the stone columns.