Experimental Study on the Relation between the Sediment Movement and the Channel Bed Form

Chiefly, about the form of the impermeable layer in the channel

Abstract

It was tried in th1S paper to settle the problems what would do the role of a trigger to the occurence of a mud flow in a devastated stream. For this reason, the following supposition was induced;that is to say, slide will occur in a sand layer of a channel when a ground water gets to acritical depth in which a shearing force is larger than a registance force. Forms of longitudinal and cross sections of outcropped rocks in some stream beds at Sakurajima Island were classified into the following four types;the uniformity type, the terrace type, the narrow and upheaval type, and the narrow and V shape type, .as to the sectionof the surface of the impermeable layer in a stream bed. With such models of these impermeable layers, differences among the formes of these four types were investigated as the differences of the incipient motion times of sand for flow. As the result, it was showed that the incipient motion time of sand for flow had a tendency to get short like as the narrow and V shape type>the narrow and upheaval type>the terrace type>the uniformity type. Secondly, it was showed that the increasing rate of stress, occurring in the sand layer, to the time and that of pore pressure would be of the same character, and the ratio of Δp/Δt of the terrace type, the narrow and upheaval type, the narrow and V shape type to that of the uniformity type were generally larger than unity, there was a tendency that the increase of the pore pressure in the terrace type, the narrow and upheaval type, the narrow and V shape type would be more rapid than that of the uniformity type.