One of the recent techniques for soil improvement is unconnected stone columns embedded in soft/medium clay. Stone columns are excellent when compared with other ground improvement techniques, with respect to coast and durability. So, it is important to determine the parameters affecting the capacity of the unconnected stone columns which in turn strongly affect the total cost of foundation works. This study had two main objectives; the first one is to establish a numerical model to predict the optimum length, spacing and diameter of unconnected stone columns used to improve the clayey soil. Also, the second is to study the effects of different studied parameters on the stone columns capacity and settlement. The analysis was carried out using finite element analysis PLAXIS 3D.The model is capable to determine the bearing capacity and settlement for different parametric analyses. A parametric study was performed applying the established numerical model. The studied parameters included stone columns, other clayey soil parameters and also specific parameters of the cushion that may be found between the footings and clayey soil improved using stone columns. The stone columns diameter, length, material and spacing were considered in addition to the shear strength of the surrounding clayey soil. Regarding to the cushion, its thickness and material were taken into consideration in the parametric study.