In the elastic beam method for the design of sheet pile quay-walls, the sheet-embedded ground are divided into many layers.
　The dynamic behavior of each layer is elsto-plastic. It behaves elastically until it reaches to the constant deformation S (spring constant k). It behaves plastically over S and the ground reaction is constant. S and k may be different in another layer. The solution for elastic beam in the condition of such ground model could be got, using the electronic computer. In the comparison with actual quay-walls, it gives consistent result.