The effect of sediment properties such as shape, size, specific weight and packing (support) condition on the incipient motion of large solitary particles was systematically investigated. A series of experiments was conducted in a rectangular tilting flume with a smooth fixed (rigid) bed under uniform flow conditions. In each experiment, a thin fibreglass rectangular rod of height 1/5 or 1.5/5 of the height of the particle was placed just downstream of the particle to imitate the interaction of particles in rivers. Contrary to common belief and knowledge, it was found that the Shields parameter decreased as the dimensionless grain diameter increased for a given bed slope under rough turbulent flow conditions. Moreover, a larger shear stress was needed to start the motion of particles on steeper slopes for a given particle diameter. An increase in the ratio of the support height to particle height by 50% resulted in an increase in the dimensionless critical shear stress by almost six times for the same particle and relative roughness.

中文翻译：

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沉积物性质对固定床上大孤立颗粒初运动的影响

系统地研究了形状、尺寸、比重和填充（支撑）条件等沉积物特性对大的孤立颗粒的初始运动的影响。在均匀流动条件下，在具有光滑固定（刚性）床的矩形倾斜水槽中进行了一系列实验。在每个实验中，将一根高度为颗粒高度 1/5 或 1.5/5 的细玻璃纤维矩形棒放置在颗粒的下游，以模拟河流中颗粒的相互作用。与普遍的看法和知识相反，我们发现，在粗糙湍流条件下，对于给定的床坡度，屏蔽参数随着无量纲颗粒直径的增加而减小。此外，对于给定的粒径，需要更大的剪切应力来启动颗粒在更陡峭的斜坡上的运动。