Abstract

Stone columns are known to be a cost effective and environmental friendly ground improvement technique, which is widely used to enhance the performance of shallow foundations built on soft ground. Stone columns increase bearing capacity, reduce settlement, reduce significantly the consolidation period and minimize the liquefaction potential of the ground. The current design of these columns is generally based on theories developed for single columns, ignoring the group interaction and accordingly the group efficiency. In the literature, reports can be found to confirm that the failure of single stone column is mostly due to bulging, meantime for a group of stone columns, the failure mechanism takes place by massive shear failure of the group and the surrounding soils. The objective of this thesis is to develop a numerical model, based on a two dimensional finite element technique. The model is capable to identify the different mode of failures of single and group of stone columns for a given columns/soil/loading condition. In these cases, group interactions were examined and evaluated. Parametric study was conducted on the parameters believed to govern this behavior. The results produced in this study showed that ground reinforced by group of stone columns may fail by general, local or punching shear failure, depending on geometry of the group and properties of the surrounding soils. Analytical models were developed for the ultimate bearing capacity of single and groups of stone columns. The models take into consideration the column interaction among the group and the strength of the surrounding soils and accordingly depict the appropriate mode of failure. Furthermore, analytical model was developed for the prediction of settlement of foundations under single or widely spaced stone columns. The design theories are provided with design procedures and charts for practical use.