Changing impermeability boundary conditions to obtain free surfaces in unconfined seepage problems

A coupled numerical model of flow through porous media, formulated in terms of the fluid displacements and changing the impermeability boundary conditions, is applied to calculate the free surface in unconfined, steady-seepage problems. In this new methodology, the domain of computation is kept constant, and the free surface is iteratively obtained by imposing impermeability conditions at the free boundaries, which are updated at the end of each iteration, aiming to simulate the physics of the problem. By doing so, a line of pore-water pressure equal to zero (free surface) is obtained in a few iterations, usually two or three. The results obtained with the proposed method have been successfully compared to analytical and numerical solutions in several examples to show the usefulness of the method in practical seepage problems.