<p>Stone columns are widely used around the world as a cost-effective soil improvement technique for highways and embankments. They are also used as drainage to expedite the consolidation period of soft clay, and accordingly to increase the shear strength, to reduce settlement and liquefaction potential. Currently the design of these columns is based on the unit cell or homogenized material concept, which overlook the effect of the interaction of columns within the group. A prototype experimental setup was developed to simulate the case of soft clay reinforced with a group of stone columns. The setup consisted of a triaxial facility, consolidation tank, hydraulic loading system and reaction loading frame. The test commenced by filling the consolidation tank with the laboratory prepared clay. At the end of the consolidation process a group of stone columns was installed into the clay. Blocks of a stone column together with the surrounding clay were extracted from the consolidation tank for testing in the triaxial chamber. The results support the existance of column’s interaction and a group of stone columns may fail by general or local shear, while a single column may fail by bulging. Furthermore, the level of improvement increases with the increase of the replacement area, while spacing and diameter of columns have little effect on the level of improvement. An improvement factor was introduced as “IMF”.</p>