Mode of Failure of a Group of Stone Columns in Soft Soil

The design of stone columns is currently based on theories developed for a single column, ignoring the group interaction and therefore the group efficiency. Whereas single stone columns mainly fail by bulging, a group of stone columns may fail by bulging or shear of the entire soil/columns mass. A numerical model was developed to simulate the case of a single stone column and a group of stone columns installed in soft clay. The model establishes the level of interaction between individual columns and therefore determines the mode of failure of a given geometry, soil, and loading condition. The model was validated with the available experimental data in the literature and used to generate data for a potential mode of failure. This parametric study is conducted to examine the effect of the parameters believed to govern the mode of failure and includes modulus of elasticity of the stone column material and the clay, column diameter, and the spacing and angle of shearing resistance of the column material. The design procedure is presented to assist the designer in establishing the mode failure of a group of stone columns (bulging, general, local, or punching shear). (C) 2013 American Society of Civil Engineers.