Two-dimensional deep-seated slope stability analysis of embankments over stone column-improved soft clay

A two-dimensional (2D) finite difference method was adopted in this study to estimate the factor of safety (FS) against deep-seated failure of embankments over stone column-improved soft clay based on individual column and equivalent area models. In the equivalent area model, the equivalent parameters (unit weight, cohesion, and friction angle) for the improved area were estimated based on the area average of the parameters from stone columns and soft clay. The factors influencing the FS against deep-seated failure of embankments over stone column-improved soft clay were investigated including the spacing, size, and friction angle of stone columns, cohesion of soft clay, friction angle and height of embankment fill, and existence of ground water. Based on the numerical results, a reduction factor was proposed to account for the difference in the FS when the individual column model is converted to the equivalent area model. The effects of the influence factors on the reduction factor were also investigated. The comparative study shows that the FS values obtained by the equivalent area model are higher than those by the individual column model. The results of these analyses are summarized into a series of design charts, which can be used in engineering practice. A reduction factor for FS of 0.90 is appropriate to convert the calculated FS by the equivalent area model to that by the individual column model based on the current study. Furthermore, the existence of the water table results in lower FS values than the cases without considering a water table because the groundwater reduces the shear strength of the improved foundation.