Numerical analysis of vertically loaded rammed aggregate piers and pier groups

Predicting the effects of piers in settlement control and capacity enhancement of foundations supported by rammed aggregate piers (RAPs) is an important aspect in design of these foundations. To quantify these effects, employing the finite-element approach, a series of three-dimensional elasto-plastic numerical models of RAP foundations were developed. To take into account the influence of radial stress development in the matrix soil during the ramming process, which forces aggregate downwards and outwards into the borehole wall, the cavity was expanded both in radial direction and downward at the base of the pier. Using a parametric study, the effects of some parameters such as piers slenderness, the ratio of piers area to the foundation area and soil properties on static behaviour of such a foundation system were investigated. Using the results of the parametric study conducted on single piers, the research aimed also to provide new insights into the group behaviour of piers when they are subjected to vertical loads. The results demonstrated that the dominant deformation of piers in group is a tendency to tip-stress behaviour. Based on the results provided in this study, which were focused on the load-settlement behaviour of RAPs-supported foundations, a settlement-based design procedure was presented for RAP systems in which the values of slenderness and the area ratios are determined.