細砂入滲理論及動態模擬

Theory and Dynamic Simulation of Fine Sediment Infiltration

衛紀淮(Ji-Huai Wei)

指導教授 ： 李鴻源

國立臺灣大學/工學院/土木工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02315

摘要

水庫壩體的存在價值及必要性，隨著社會發展及對於生態面向的考量逐漸增加而產生改變。近年來移除壩體相關研究越來越受到重視，其中壩體移除影響層面多而廣，尤以泥砂問題最為廣泛，而其中細砂入滲影響到棲地之條件，是一個極為重要議題。細砂入滲相關研究中，主要都是實驗室和現地實驗，相關的理論較不完備。而在近幾年，Wooster et al. (2008)做一較完整的細砂入滲實驗，Cui et al. (2008)依據物理概念所推導的理論也與之相符，但其只在細砂入滲達飽和時與實驗驗證，在未飽和前，細砂入滲隨時間之動態變化關係尚未明確。由於近年來電腦運算速度的進步，越來越多顆粒運動的研究，可使用運算量較大的離散元素法來模擬；本研究將細砂入滲視為多顆粒運動行為，在礫石及細砂粒徑分別約為10mm及0.35mm之尺度下，沉降現象為細砂主要的運動機制，而碰撞力、摩擦力描述顆粒間之交互作用，細砂產生阻塞則跟摩擦力的大小及礫石及細砂在空間中的分佈有關。在此架構下，使用離散元素法PFC3D模擬，模擬結果與Wooster et al. (2008)的實驗結果驗證良好。最後將動態的模擬結果與Cui et al. (2008)的理論相比較，發現Cui et al. (2008)的理論中，有一些不盡合理的假設，包括表面入滲通量恆為定值及阻塞係數隨細砂入滲比例增加而增加；然而，阻塞發生時，會造成入滲通量減小；且由於粗顆粒分佈的不均勻，留下孔隙較大的區域，阻塞效果反而會減少、阻塞係數變小，這也是造成上下層停止入滲時有一相位差的原因。

關鍵字

細砂入滲 ； 離散元素法PFC3D ； 數值模擬 ； 阻塞效應

並列摘要

The existence and necessity of reservoir and dam today is changed with the gradual increase of social development and eco-oriented considerations.
The issues about dam removing has been duly noted in the recent years, the influence of dam removing is wide-ranged, especially in the sediment problem.
Fine sediment infiltration is an significant topic since it affect the habitat environment seriously. Nevertheless, fine sediment infiltration studies are mainly focus on laboratory experiments and situ experiments, and less discuss in theoretical problems.
Recently, Wooster et al. (2008) had performed a completely fine sediment infiltration experiments, and Cui et al. (2008) had a theoretical derivation based on the physical concepts is conform with the Wooster et al. (2008) experiment data, and Cui et al. (2008) is only verified on the saturated of fine sediment infiltration since the data from Wooster et al. (2008) are all saturated, Therefore the dynamic changes of unsaturated fine sediment infiltration over time is not clear.
Recently the improvement of computing speed, more studies of particle motion could be simulated by discrete element method, which needs a large amount of computation to simulate. In this study, the fine sediment infiltration is regard as a multi-particle motion behavior in the gravel and fine sediment particle size of about 10mm and 0.35mm of scale, the subsidence phenomenon is the main settlement mechanism, while the collision force, friction describe the interaction between the particles, and trapping of fine sediment is related to the friction and gravel and fine sediment’s distribution in space.
In this framework, using the discrete element method PFC3D’s analog simulation and compare with Wooster et al. (2008) results are well verified.
Finally, compare with the dynamic simulation results and Cui et al. (2008) dynamic theory, find out that Cui et al. (2008) theory exist an unreasonable assumptions including surface infiltration flux setting and trapping coefficient with fine sediment infiltration proportion increases.
However, when trapping occurs, the infiltration flux decreased, and due to the uneven distribution of coarse particles, the smaller pores fill up first, and leaves the larger pores, which reduce the trapping effect and trapping factor, that’s the reason why exists a phase difference between the upper and lower when infiltration stops.

並列關鍵字

fine sediment infiltration ； discrete element method PFC3D ； numerical simulation ； trapping effect

參考文獻

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