THE MODELLING OF THE GENERATION AND DISSIPATION EXCESS POREWATER PRESSURE IN SEABED SEDIMENTS UNDER WAVE ACTIONS

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The following subjects in the cohesive coastal sediments are included in the scope of the present research :1) Siltation induced by wave actions leading to the contamination of sea water as an important environmental problem for ports and harbors.2) Settlement and instability of breakwaters founded on soft normally consolidated clay.From the geotechnical point of view, a study of wave-induced cyclic loading and the associated effective stress regime in sediments is relevant to both of the above topics. To carry this out, the precise measurement or prediction of excess pore water pressures in coastal sediments is essential. The following conclusions were derived from a recent study :1) Based on the diffusion type of defferential equation including a term for sedimentation, a numerical model was established to evaluate the distribution of void ratio in coastal cohesive sediments under wave actions. The effect of interation between waves and silt was taken into consideration for the erosion flux. The numerical experiments were carried out under various intial conditions. The results indicate that the model is capable of predicting the approximate distribution and change of void ratio against depth during and after the sedimentation of silt.2) A model combined with Terzaghi's three dimensional consolidation theory and an empirical relation formulated from the results of undrained cyclic triaxial tests was proposed to predict the behavior of clay under partially drained cyclic triaxial tests as boundary value problem. It was also suggested that this model could estimate the long-term settlement and instability of a breakwater founded on cohesive seabed sediments under stormy conditions.