Hydraulic Interpretation of Sand Size Distributions
Hydraulic Interpretation of Sand Size Distributions
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DOI：
10.1086/628208
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发表时间：
1976-07
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影响因子：
--
通讯作者：
G. Middleton
中科院分区：
文献类型：
--
作者：
G. Middleton
在概率纸上绘制（使用φ变换）时，粒度分布通常显示不连续性和直线段。组成分布的不同成分通常被解释为由不同运输机制移动的颗粒亚群。本文认为这一假设的限制情况下观察到的两个粗粒组分在许多样品的河床材料。通过对河床物质和悬移质的比较分析，表明这些组分可以解释为（C）牵引力和（A）间歇性悬浮物亚群，由河流的主导流量移动。本文通过对明渠紊流的理论、试验和实测资料的分析，提出了一个比较满意的分离两种输沙机制的近似水力学判据：当颗粒的沉降速度大于水流的剪切速度时，颗粒的运动是牵引运动;当颗粒的沉降速度小于水流的剪切速度时，颗粒的运动是间歇悬浮运动。通过与中卢普河、尼奥布拉拉河、埃尔克霍恩河、密苏里州河、密西西比河和格兰德河的水力和沉积物数据进行比较，证实了这一标准。因此，应该可以通过确定两个粗粒组分之间的“断裂”尺寸来确定古河流砂的主导剪切速度。
Grain size distributions commonly show discontinuities and straight line segments when plotted (using the phi transformation) on probability paper. The different components making up the distribution have commonly been interpreted as subpopulations of grains moved by different transport mechanisms. The paper considers this hypothesis for the restricted case of the two coarsest components observed in many samples of river bed materials. By comparing analyses of bed materials and suspended load, it is shown that the components may be interpreted as (C) traction, and (A) intermittent suspension subpopulations, moved by the dominant discharge of the river. From an analysis of theory, experiments and field data on turbulence in open channels, it is shown that a satisfactory though approximate hydraulic criterion for separating the two mechanisms of sediment transport is as follows: grains move by traction if their settling velocity is larger than the shear velocity of the stream, and by intermittent suspension if their settling velocity is smaller than the shear velocity. This criterion is confirmed by comparison with hydraulic and sediment data for the Middle Loup, Niobrara, Elkhorn, Missouri, Mississippi and Rio Grande Rivers. Consequently, it should be possible to determine the dominant shear velocity of ancient fluvial sands by determining the size "break" between their two coarsest components.