This paper describes the development of a two-dimensional soil-structure interaction model based on the finite element method for calculating the structural design parameters (i.e., moments, shears, and deflections) in a raft foundation (stiffened or constant thickness) resting on expansive soil. The model is capable of estimating the distorted mound shape by considering the soil suction distribution differences throughout the supporting soil mass and the associated volume changes (shrink/heave) with respect to time under a set of different edge conditions. The model requires only a statement of the initial soil suction conditions in the supporting expansive soil mass and the changes in the boundary conditions to predict the response of the raft foundation to these boundary condition changes. The model has been shown to yield results that agree well with reported field measurements of surface volume changes (shrink/heave)