Numerical Study of the Failure Process of Stone Column Groups in Soft Soil in Response to Rigid Loading Based on the DEM-FDM Coupled Model

Compared with isolated stone columns, a group of stone columns exhibits a much more complicated failure mechanism because of the complicated interactions between the respective columns and the surrounding soil under various loadings, as well as the influence of the relevant geometries. Here, a numerical study based on the discrete-element method and finite-difference method coupled model was conducted to simulate the complete load-bearing process of stone column groups and to better understand the deformation and failure mechanisms of stone column groups in soft soil in response to rigid loading. The load settlement curves for the columns, soil, and loading plate were determined as the displacement and stress evolution. Moreover, the shear strain distribution indicating the ground failure mode during the complete loading process was visualized. Parametric studies considered the influences of the column arrangement, the soil strength, and various stiffnesses. The bearing capacity of individual columns within a stone column group varies due to the differing stress states of the surrounding soil. Edge columns typically fail first, thus transferring load to the internal columns. With a smaller number of columns, transferred loads can trigger internal column failures, resulting in overall instability of the column group. The strength and stiffness of the surrounding soil govern the stone column–bearing capacity. However, existing bearing capacity formulas primarily rely on soil strength parameters, ignoring the significance of soil stiffness.