2014 年 70 巻 2 号 p. I_738-I_743
This paper describes the results of experimental investigations of sediment transport and topographic change in mixed soil conditions exposed to steady flow in an open channel and regular waves in a wave flume with a tidal flat structure to understand the influence of cohesive sediments on sediment transport in cohesive and non-cohesive sediment mixtures. In the open channel experiments, the sediment transport rate q was investigated with the influence of clay and steel slag increasing resistance force by cohesive effects and surface roughness adding to sand on sediment transport under the same hydrodynamic condition. From the results, both the steel slag and clay mixtures decreased q and the effects of a decrease in q for steel slag mixtures were larger than that for clay mixtures in the same content ratio pf. The wave flume experiments showed the opposite crown migration between sandy and sand-clay tidal flats. In the sandy tidal flat, an increase in wave height led to increasing shoreline retrogression and broadening eroded area in the early stage expanded with ripple formation during experimental time. However, in the sand-clay tidal flat, the topographic change was characterized by the little topographic change without ripple formation in the early stage, the advanced crown in the final profile, and the loss of clay on the surface layer of the tidal flat with time. Since a modified critical Shields parameter considering cohesive force showed better performance to evaluate sediment transport in sand-clay mixtures, it was required to take into account cohesive effects when discussing the sediment dynamics in mixed soil conditions.