In this thesis, a novel approach to account for the soil nonlinearity of nonhomogeneous soil deposits by employing the modified Vlasov foundation model is developed. A new algorithm that takes the modulus degradation curves at varying strain levels into account in an iterative manner is obtained by modifying the previously developed formulation. The presented model will provide researchers with the opportunity to employ the experimental test data directly for an operational strain level that may occur in many foundation engineering designs. This new model which takes the nonlinear soil behavior into account is first verified against the linear model given in the literature to ensure that the new model algorithm can capture the linear solution when the soil behavior is assumed to be linear. Later, the experimental data of modulus reduction curves reported in the literature for a specific type of dense and loose sands are used in multiple foundation deflection analyses. Example problems are considered for different cases which presented: (i) how the model captures nonlinear behavior and (ii) the significant effect of the nonlinear soil behavior on deflection, moment, and shear force. The model results are also compared with the finite element model result, assuming a bilinear stress-strain soil model. The results obtained from both models matched well, especially for the maximum deflection values that occurred in the example problems.