This study investigates the behavior and bearing capacity enhancement of composite concrete–stone columns used for ground improvement in soft clay soils, where conventional stone columns often suffer from limited lateral confinement and reduced efficiency. A numerical analysis was conducted in PLAXIS 2D (version 20) and validated using the experimental results of A. P. Ambili and S. R. Gandhi to ensure reliability of material properties, geometry, and boundary conditions. Following validation, four configurations of composite columns with concrete segments varying from 0.5 to 2.0 times the column diameter were analyzed to evaluate the influence of the concrete length on vertical stress distribution, stiffness, and deformation characteristics.The results demonstrate that increasing the length of the concrete segment significantly enhances the column’s stiffness and vertical load-carrying capacity. When the concrete part reached half of the total column length, the vertical stress at 30 mm settlement increased from approximately 1000 kPa (for a conventional stone column) to about 2000 kPa. Analysis of lateral deformation showed that maximum bulging occurs at a depth close to one diameter from the top of the column. Incorporating a concrete segment reduces bulging by 15–50%, depending on the concrete length, and bulging becomes negligible when the concrete segment exceeds 1.5 diameters. These findings confirm that the concrete portion forces the bulging zone deeper, where confining pressure is higher, thus improving failure resistance. Overall, composite concrete–stone columns exhibit superior bearing capacity, reduced deformation, and improved resistance to bulging failure compared with both traditional stone columns and bored piles of similar dimensions.
Hani Mohammed Abdo Sharaf (Thu,) studied this question.