Effect of vibro stone column installation on the performance of reinforced soil

Empirical design methods for stone column foundations are often on single stone columns or as a homogeneous medium of soil/column. These methods underestimate the capacity of the composite system because they do not take into account the increased confining stress acting on the stone column or the increased stiffness of the soil. This study used Plaxis 2D to study the effect of the installation method on the confining pressure and soil stiffness around a single column by assuming the installation of the column could be modelled as an expanding cavity followed by consolidation of the surrounding soil. The mean stress and stiffness generated during installation between two, adjacent columns was used in Plaxis 3D to compare the settlement of circular foundations on estuarine deposits reinforced by stone columns at a site in Santa Barbara, California. Good agreement was found between the predicted and actual settlement of the trial foundations on three column arrangements. The predictions gave a better estimate of the settlement compared to those using a unit cell or homogeneous medium showing that improvements to the soil should be taken into account when assessing stone column performance.