This paper suggests a new method of computing interior forces and deformations of the base-slab of a dock settling basin. The base element is considered as a finite beam under the action of bending supported by subgrade soil. The deformation of the subgrade is determined through the Fuss-Winkler model. The basic parameter (i.e., coefficient of subgrade reaction) of this model is a nonlinear parabolic equation along the length of the beam. The solution of this model leads to an ordinary differential equation that can be solved by using boundary conditions and Picard limit of a sequence method. After the solution of the equation, the deformations and interior forces are computed at any arbitrary cross section of the beam and the results of this study are compared with the other methods offered in the literature and compatible outcomes are achieved.