An elasto-plastic soil model, which takes viscous damping into account, is proposed for coupling VOF model to analyze the dynamic behavior and deformation of structure and seabed under wave actions including impulsive load conditions. The validity of the model is verified by use of experimental results on dynamic response to an impulsive breaking wave and observed response to swell for composite breakwaters. By application of the model, it is found that soil is likely to come to plastic condition under the caisson due to its surge and pitch motions at wave crest. In addition, the progressive deformation due to repetitive wave actions and residual deformation of the structure are analyzed.
