Abstract This paper reports on an experimental study conducted on a soft cohesive soil improved with stone columns. The load–deformation behavior of the soil specimen has been captured by varying the number of columns, foundation shape, and stones’ particle gradation. A uniform soil bed has been prepared under controlled density and moisture conditions inside a cubic steel tank and stone columns have been installed. Keeping the vertical compressive load, length, and diameter of stone columns constant, five different stone sizes of uniform gradations having average particle sizes ranging between 1.5 and 11 mm have been examined. Load tests are performed using square- and circular-shaped footing plates, and the physical models have been subsequently simulated using the finite element method. The analysis of results revealed that the foundation shape has insignificant effect on current small-scale model testing, but it may be significant at magnified scale. With the increase in particle size, a better reduction in settlement could be achieved, thus implying better improvement. Observed results indicated settlement of a single column is governed by both punching and bulging of column, whereas in a group, the major settlement takes place because of punching into the soil. Nevertheless, this study provides verified and comprehensive frameworks for both physical and numerical model testing of different soils improved with stone columns that would directly benefit practitioners to optimize a site-specific soil improvement program involving the use of stone columns.