Abstract: Wrapping the individual stone columns with vertical geosynthetics can effectively improve the load performance of stone columns and control the settlement of composite foundation. The quantitative improvement of loading capacity of geosynthetic-encased stone columns is investigated through two series of laboratory model tests conducted on stone columns installed in soft soils in a large scale testing tank. Bugling failure models and reinforcement mechanism are discussed, and the stress-strain characteristics of vertical encasement are analyzed. The results from the loading tests indicate significant improvement in loading capacity of the stone columns due to vertical encasement. The biggest bugling deformation occurs just below the encasement, and the bugling model involves the interaction between the stone column, vertical geosynthetic-encasement and surrounding soils. The column-soil stress ratio of composite foundation for the encased stone columns is much higher than that for the ordinary stone columns. The vertical geosynthetics greatly improve the stiffness of stone columns and help to transfer the upper load to the bottom layer of soils.