Numerical Study on Bearing Capacity and Bulging of the Composite Stone Column

In weak clay soil, a proper ground improvement technique using a stone column can be limited by the absence of sufficient lateral confining pressure. Stone columns should be strengthened to provide the minimum required lateral confining pressure.

The aim of this study is to find out the significant improvement of the composite stone columns compared to the conventional stone columns by comparing the bearing capacity enhancement and the treated soil stiffness for both models. Composite stone columns with a solid concrete part at the top-head not only enhance the bearing capacity of the stone columns but also decrease the bulging failure and increase the surrounding soil stiffness.

The 2D finite element analyses were carried out to simulate an experimental study conducted by Ambily and Gandhi on conventional stone columns. ABAQUS software program with the Mohr-Coulomb criterion for soft clay soil and stones was used in the simulation. First, a preliminary numerical model was created to simulate the experiment model. Similar material properties, boundary conditions, and constraints were considered in the preliminary model. The results were compared, and they were similar to the experimental results. During this process, the efficiency of the numerical model was confirmed. Second, the same numerical model was performed for the composite stone columns without modifying the material properties, boundary conditions, and constraints of the preliminary model. The parameters that influence the composite stone column bearing capacity as the length of the concrete part, the stress concentration ratio, and the shear strength of the surrounding soil, were all studied.

The data obtained from the aforesaid study was used along with ABAQUS software package. Compared to existing work, our approach achieves a significant correlation, and it indicates that the solid concrete part increases the surrounding soil stiffness, in addition to increasing the bearing capacity of the stone column. The solid concrete part resists bulging deformation by moving the bulging failure downward where the confining pressure is larger. The stress concentration ratio increases with the length of the solid concrete part.

Composite stone columns have a significant influence on the improvement of weak clay soil and increase the bearing capacity of soil under superstructures. Furthermore, they also increase the stiffness of weak soil around the column. The magnitude of weak soil improvement by using composite stone columns is greater than conventional stone columns. Therefore, composite stone columns are more efficient and effective than conventional stone columns.