A Flume Study on Grain Size Distributions of Sediments and Patterns of Heavy Mineral Concentrations
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摘要: 大型室内水槽重复实验表明，在顺直河道中，分选作用导致了从上游至下游表层沉积物粒径变细、重矿物含量增加。不同河床微地形对重矿物的富集能力不同。在平面上，深槽和浅滩迎水坡为重矿物富集区。在剖面上，则存在表层富集层、埋藏富集层和残留富集层三种富矿层。重矿物在河道中的富集规律表明。侵蚀作用在重矿物富集过程中扮演着重要色。Abstract: The flume study was made at Environment Research Center of Tsukuba University, Japan. The observation of the bedload transportation and the grain size analysis of samples collected along the channel from upper to downstream showed that selective sorting plays a very important part in heavy mineral concentrations. The results were as follows: 1) The sediment from superficial layer was fining downst reamward. As a result, the percentage of heavy mineral fractions increased with increasing distance off the flume inlet. The longer the distance, the higher the percentage was. The maximum reached 48% near the flume outlet, whereas the initial population was lower than 5%. 2) Heavy particles were characterized by good sorting and fine diameter size. Mean particle size ranged from 1.5 to 2.5φ. Major content was fine sand. 3) The percentage of the heavy mineral fractions changed with the variation of bedforms. Stoss side of a bar, trough and pool were traps of heavy particles. 4) According to the texture of the sediment, a bar was divided into three parts. The superficial layer of the tail was observed to contain large amount of fine and medium sand and to be rich in heavy minerals. In contrast, the head of a bar was mainly composed of gravel and coarse sand, which contains few heavy particles. The body of a bar mediated between the tail and head. 5) On transection, three layers with abundant heavy minerals were observed, but only the lag layer was continuous and signified to forming placers.
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Key words:
- straight stream channel /
- grain size /
- heavy mineral
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