*Ps* = − ∗ − ∗+ ∗− ∗ + ∗+ ∗ **2604 10412 A 11440 B 4034 C 2568 D 1420 E 133 F** (2)

And it can be represented by another suggested model of Quadratic form.

The equation can be used to predict the response for each factor levels, that should be specified by their original units. Because the coefficients are scaled to accommodate the factor units and the intercept is not at the center of the design space; this equation is not able to be used in determining relative impact.

**Figures 9**–**11** shows the response surfaces describing the swelling pressure Ps dependence on, the Dry unit weight (kN/m3 **)** and the water content w (%), plasticity index (%) and Dry unit weight (kN/m3 ) and the degree of saturation (%) respectively. Plasticity index (IP) and water content (w) and the preconsolidation pressure, the dry unite weight and the swelling index for this case study.

**Figures 12** and **13** represent the factors that affect the (Ps) where the plasticity index is fixed common parameter, saturation degree and the preconsolidation pressure varied respectively.
