Research on Sediment Transport Rate in Surf Zone by Taking Account of Liquefaction and Fluidization of Sand Layr

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In this research, the layred motion ( sheet flow ), which is a typical type of sediment motion in surf zone, is treated. The purpose of the research is to make clear the effects of the porewater pressure and the vertical effective stress variation on the layred motion, find the constitutional equations and obtain a law of sediment transport rate in surf zone.In order to reproduce the porewater pressure variation in a normal sand bed in laboratory, it is necessary to generate simultaneously a water pressure variation and a oscillatory flow as large as the wave pressure and the oscillatory flow on seabed in actual coast. For this purpose, an oscillatory tube of U shape with both ends closed was developed. Unfortunately, with the limited budget, the desired large pressure variation and oscillatory flow and a free control of the phase between the pressure and flow could not be obtained.The porewater pressure variation in a thin layr of 10cm below the sand bed surface, which is important for the layred motion, was measured under only a water pressure variation in this tube. The measured results were compared with an approximate solution, and the values of constants in the solution were discussed. Also the subsidence of a block on a sand bed was measured under a water pressure variation and an oscillatory flow in the tube. The effects of the wave pressure and the oscillatory flow on the subsidence were discussed.Several other works were done. Among them, a new more effective oscillatory tube was developed. At present, the research is continued using this new tube to obtain the law of sedimenet transport rate in surf zone. A new numerical simulation technique is also being developed by applying the so-called distinct element method.