考慮泥砂安息角於局部沖刷坑數模之研究

Study on Numerical Model of Local Scour Considering Sediment Repose Angle

藍尹圻(Yin-Chi Lan)

指導教授 ： 葉克家 ； 廖仲達

國立交通大學/工學院/土木工程系所/碩士(2018年)

摘要

台灣河川具有坡陡流急，洪水期間沖淤變化劇烈之特性。為了降低易致災河段發生災害的風險，常需考慮建置水工建造物並檢討其設置前後對河防安全之影響。然目前國內相關研究中，當模擬範圍具有丁壩、橋墩、固床工等涉及三維流場問題時，仍受限於三維模式計算不易收斂或計算時間考量等，多採用水平二維模式進行相關分析，基於水深方向平均之假設，當水深方向之流速分布差異明顯時，模擬成果常有其不確定性與限制性。
本研究結合丁壩局部沖刷坑形成機制及泥砂安息角經驗式，開發二維動床模式之局部沖刷坑修正機制，藉由CCHE2D模擬實驗室丁壩試驗及現場濁水溪香員腳堤防丁壩案例，進行丁壩局部沖刷過程之檢定、驗證與比較分析，探討泥砂安息角對構造物局部沖刷之影響，以提升二維動床模式模擬相關問題之準確性。
二維動床模式加入本研究修正機制後，可有效提升不同空間尺度案例中，丁壩局部沖刷坑之模擬準確性。由實驗室與現場沖刷案例之模擬結果可知，在丁壩沖刷過程中，刷坑內泥砂粒徑係逐漸粗化，產生不同泥砂粒徑組成，壩頭上游側較陡之刷坑坡面，受泥砂安息角因素影響最大。

關鍵字

丁壩 ； 局部沖刷 ； 泥砂安息角 ； CCHE2D

並列摘要

Steep slope and severe bed change are the general characteristics of Taiwan’s rivers. In order to reduce the risk of disaster, it is an important issue to analysis the impact of local scour around the hydraulic structures on the channel. However, the two-dimensional mobile-bed models are widely used for complex three-dimensional flow field and local scour problems, such as the vicinity of piers, spur dikes, aprons, etc. It is inadequate because of the use of section-averaged or depth-averaged velocity, in the case where the flow velocity distribution along the direction of water depth is significantly different.
In this study, a mechanism for improving the local scour around structures in the two-dimensional mobile-bed model is proposed. The sediment repose angle formula is included in the mechanism. The CCHE2D model is selected to simulate the experimental case and Xiangyuanjia Embankment case in Zhoushui River for the model calibration, validation and comparison.
When the proposed mechanism is included in the two-dimensional mobile-bed model, it can improve the simulated accuracy of the local scour around spur dikes in different scale cases effectively. According to the simulated results of the experimental and field’s cases, the sediment particle size of the scour hole is gradually increased during the scouring process. The scour hole side slope is steep at upstream of the spur dike, it is most affected by the sediment repose angle.

並列關鍵字

spur dike ； local scour ； sediment repose angle ； CCHE2D

參考文獻

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2. Brownlie, W. R. (1981). “Compilation of fluvial channel data: laboratory and field.” Rep. No. KH-R-43B, W.M. Keck Lab. of Hydr. and Water Resources, California Institute of Technology, Pasadena, Calif.

3. Copeland, R. R. (1983). “Bank protection techniques using spur dikes.” Engineer Waterways Experiment Station, P. 0. Box 631, Vicksburg, Miss, 1-132.

4. Dey, S. (2001). “Experimental studies on incipient motion of sediment

particles on generalized sloping fluvial beds.” Int. J. Sediment Res.,