Coastal structures are always facing the threat of damage caused by different wave actions. A better understanding of different seabed behavior could effectively reduce the damage caused by waves. In this paper, a 2 Dimensional quasi-dynamic u-w-p model is developed to analyze the different behaviors of seabed composed of loose sand, dense sand and silt. In the u-w-p model, acceleration, velocity and displacement has been considered, and three important parameters: pore water pressure, effective stress and shear stress, are obtained from the model with Finite Difference Method (FDM) and applied to describe the general behavior of seabed consisting of various materials. The results indicate that denser and more uniform soil structure and lower permeability could highly increase the stability of seabed, which means a lower probability of having liquefaction or shear failure inside the seabed. In addition, the phase lag plays a more important role in loose sand seabed than in the other types of seabed. This paper presents a comparison study of wave induced stress variation in seabed between fine-grained soil and coarse-grained soil, and provides a view differing from some of the published literature on seabed.

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