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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Quantifying gravel overlap and dislodgement forces on natural river bars: Implications for particle entrainment
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Quantifying gravel overlap and dislodgement forces on natural river bars: Implications for particle entrainment

机译：量化天然河道上的砾石重叠和移动力：对颗粒夹带的影响

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Equations for predicting particle entrainment typically assume that clast weight is the only factor resisting motion in the force balance on individual grains. In this work, increases in the force required to dislodge surface particles due to overlapping by surrounding clasts is quantified. Field data were collected at two subaerially-exposed bars along the Colorado River in central Texas, USA, with median gravel diameters (D _(50)) of 37 and 64mm. Clast size, shape, weight, the force required for vertical removal, and the fraction of clast area covered by surrounding grains were measured. Small hooks were glued to individual clasts without disrupting their positions and quasi-static peak forces required to vertically dislodge each clast were measured using a force gauge. Clasts were also colored with dye before being dislodged, and image analysis was used to calculate the fraction of clast surface area covered by surrounding grains. The effect of overlap on the particle force balance is quantified by defining the 'excess force ratio' as the dislodgement force divided by the weight of the clast. Excess force ratio varies weakly but systematically with clast size: lifting larger clasts can require forces up to two times the clast's weight, while smaller clasts can require forces up to seven times their weight. The fraction of clast surface area covered by surrounding particles is also weakly correlated with excess force ratio. By assuming that critical shear stresses are proportional to the excess force ratio, the effect that overlap alone may have on particle entrainment is calculated. For a given size class, the most mobile grains should have critical shear stresses controlled only by their weight. However, clast overlap also causes broad distributions of critical stresses for partially-exposed surface grains. The data quantify the significant fraction of bed area that should be less mobile than grain size alone would predict.
机译：用于预测粒子夹带的方程式通常假定，碎屑重量是抵抗单个谷物上的力平衡中运动的唯一因素。在这项工作中，量化了由于周围碎屑的重叠而导致清除表面颗粒所需的力的增加。现场数据是在美国得克萨斯州中部的科罗拉多河沿两条暴露于地下的钢筋收集的，砾石的中值直径（D _（50））为37和64mm。测量碎料的大小，形状，重量，垂直去除所需的力以及被周围谷物覆盖的碎屑区域的分数。将小钩子粘在单个夹板上而不破坏其位置，并使用测力计测量垂直移动每个夹板所需的准静态峰值力。碎屑在移出之前也用染料着色，并且图像分析用于计算被周围颗粒覆盖的碎屑表面积的分数。重叠对颗粒力平衡的影响可通过将“过量力比”定义为位移力除以碎屑的重量来量化。多余的力比变化不大，但随刀杆的大小而变化很大：举起较大的刀杆可能需要的力是其重量的两倍，而较小的刀杆所需要的力可能是其重量的七倍。周围颗粒覆盖的碎屑表面积的比例也与过大的力比弱相关。通过假设临界剪应力与过大的力比例成正比，可以计算出单独重叠可能对颗粒夹带产生的影响。对于给定的尺寸级别，最易移动的谷物应具有仅由其重量控制的临界剪切应力。但是，夹层重叠也会导致部分暴露的表面晶粒的临界应力的广泛分布。数据量化了床面积的重要部分，其流动性应该比单独的晶粒尺寸预测的要少。

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