Laboratory Investigation of Reology and Transport Characteristics of Hyperconcentrated Flow
高含砂水流 ； 流變 ； 賓漢屈服應力 ； 輸砂 ； hyperconcentrated flow ； reology ； Bingham yield stress
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台灣本島由於地形特殊，河川特徵多為源短流急，比降陡峻。中央山脈為台灣河川主要發源地，地質較鬆軟脆弱，台灣位於歐亞大陸板塊及菲律賓海板塊之間，以致於地震頻傳，加上人為對森林任意採伐、開墾，地表覆蓋因而遭到破壞，使水流蘊藏較高之沖刷潛勢。每逢颱風暴雨侵襲，大量沖蝕崩塌對河道屢生衝擊，而發生高含砂水流之災害亦時有所聞。台灣現有水利設施多以一般明渠流設計，高含砂水流與一般挾砂水流之性質有相當大之差異。因此，深入瞭解高含砂水之流動特性和運動機理，有其必要性。 本研究藉由東埔蚋溪初鄉橋崩塌地採集之土樣進行物理試驗，以瞭解其土壤特性，將採集之漿體調配濃度分別為24 ％、30 ％、40 ％與50 ％ 之試樣，以Brookfield水平旋轉式流變計，進行流變試驗。另外，本研究以東埔蚋溪初鄉橋崩塌地土壤作為水槽試驗粒料選擇之依據，利用動床渠槽進行高含砂流動試驗，採0.5 %、0.75 % 及1 %三種坡度，及兩種流量，進行垂向流速與濃度剖面之水理與泥砂量測。 經試驗推導出東埔蚋溪初鄉橋上游崩塌地細顆粒漿體之流變關係式，並將其與神木村及大陸多處漿體試驗結果進行比較，發現本研究賓漢屈服應力與體積濃度之關係，與其他資料之關係頗為一致。在流動試驗方面，為提高泥砂濃度，試驗之福祿數較高，且接近臨界流況(Fr=0.8~1.25) 流場相對較不穩定，整體而言，其底床屬過渡 (transition) 之床形。本研究除分析濃度及流速剖面外，並考量沉速、卡門常數受含砂濃度影響，分析高含砂水流之輸砂關係，並與管流試驗進行比較。
Because of special topography, most rivers in Taiwan are short and steep and carry rapid flows. Majority of rivers in Taiwan originate from the Central Mountains, which has weak geological formation. Taiwan is located between Eurasia plate and Philippine sea plate, and the earthquake occurs frequently. In addition, men’s activities in the forest areas have disturbed the earth’s surface covers, and caused higher erosion potential. The existing hydraulic facilities in Taiwan are usually designed based on the open channel flow theories. However, the characteristics of the hyperconcentrated flow is quite different from the regular sediment-laden flow. Therefore, it is necessary to thoroughly investigate the flow characteristics and the transport mechanism of the hyperconcentrated flow. In this study, soil physics tests were performed to investigate the characteristics of the soil samples collected at the upstream landslide areas near the Chu-Hsiung Bridge of the Ton-Pu-Rey Creek. The rheology tests were performed using the Brookfield DV-Ⅲ rheometer for slurry samples with sediment concentration of 24%, 30%, 40% and 50%. In addition, sediment transport experiments for the hyperconcentrated flow were conducted using re-circulating flume with movable bed. The vertical velocity and concentration profiles were measured for two flow discharges and three slopes ranging from 0.5 to 1%. The rheology relations for the samples near the Chu-Hsiung Bridge were derived and compared with those for the Shen-Mu Village and several sites in the mainland China. It was found that the Bingham yield stress and volume concentration relations were fairly consistent for these sites. In regard to the sediment transport experiments for the hyperconcentrated flow, in order to increase the sediment concentration, the Froude numbers of the experiments were relatively high and close to the critical condition (Fr=0.8~1.25). The flow fields were, therefore, relatively unstable. In general, the bed form belongs to the transitional type for our experiments. The vertical concentration and velocity profiles were analyzed with consideration of the effects of the sediment concentration on the fall velocity and von Karman constant. The sediment transport relations for the hyperconcentrated flows were analyzed and compared with the results for the pipe flows.
工程學 > 土木與建築工程