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Abstract:
The tsunami caused by the Great East Japan Earthquake of 2011 was called a black tsunami, and it was mixed with sediments, which was observed in many areas. Most of the previous studies on tsunami loading have been based on experimental and numerical calculations using fresh water, and the effects of sediment contamination have rarely been investigated. This study conducted bore-like tsunami pressure experiments with various densities to clarify the mechanism of impulsive wave pressure due to density changes. For validation, numerical calculations were performed on the same model used in the experiment, followed by calculations on local conditions. The average impulsive wave pressures of silt-mixed water, sand-mixed water, and freshwater were compared in terms of the Froude number. Under these conditions, the impulsive wave pressure due to sediment-mixed water was found to be in some cases greater than that with fresh water. The relationship between the water surface angle and wave pressure at impact was also investigated. The results revealed large variations. In silt-mixed water, the impulsive wave pressure tended to increase as the water surface angle at impact increased. Numerical results show that a 4% increase in density results in a 15% increase in maximum wave pressure. Additionally, an increase in the water surface angle was also observed. Numerical calculations performed under local conditions confirmed the increase in wave pressure due to sediment-mixed water. Wave pressure against the wall surface of the sediment mixture tends to increase but can be evaluated by the freshwater wave pressure rating index.
