2022 Volume 78 Issue 2 Pages I_187-I_192
Black tsunamis that engulfed bottom sediment were observed during the 2011 Great East Japan Earthquake, and there is concern about the effects of such tsunamis. In order to properly design coastal structures against tsunamis, it is necessary to quantitatively evaluate the impact of changes in density, viscosity, etc. due to the inclusion of bottom sediment. Most of the previous studies on the concentration of sand suspended by tsunamis have focused on relatively large grain size sand, and few studies have focused on bottom sediments with grain size of a few micrometers, such as mud and sludge. In this study, we conducted a moving-bed experiments on fine-grained bottom sediments, focusing on the sediment roll-up characteristics that lead to black tsunamis. The results suggest that the thickness of flow-induced fluidization of the bottom sediment surface layer differs depending on the water content of the bottom sediment, and that viscosity, which is strongly related to the water content of the sediment, is one of the factors controlling the thickness of fluidization.