This research aims to study the effect of stone columns on the change of settlement in clay soils. We defined the stone column and its uses , We explained the transfer mechanism of load to the soil . We spoke about important theories which discuss the settlement of clay soil reinforced by stone columns (Priebe theory) . we used the unite cell idea to study the settlement behavior in the clay soils affected by the stone column to generalize the study on unlimited loading area of clay soils , so we has been defined some of the basics which relate to the unit cell .We made a group of tests on a small model to define the settlement of clay soils in the case of absence of stone columns and in the case of presence of stone columns with different diameters to know the change of the settlement with the change of area replacement ratio inside the unite cell , then we compared the laboratory tests results with the results of Priebe (1995) .