人工湖補注地下水之力學分析

Mechanical analysis of groundwater recharge by artificial lake

林建翰(Jian-Han Lin)

指導教授 ： 蔡佩勳

朝陽科技大學/理工學院/營建工程系/碩士(2014年)

摘要

台灣位於亞熱帶地區，降雨多發生在豐水期5月~10月期間，降雨量極為豐富。但在枯水期11月~4月期間，大部份的區域降雨量卻均為貧乏，致使水資源在時間與空間上分配不均，使得鑿井抽取地下水之使用率逐年提高，然而地下水超抽的結果可能發生地下水位降低及地層下陷等問題。
由於地下水補注是非飽和土壤滲流的問題，因此本研究將以二相流模式來進行地下水補注之模擬；另外由於地下水位的升降使土壤承受加壓解壓的過程，因此土壤的體積變化可能影響土壤彈性模數之大小，所以將以雙降伏模式來模擬此一力學行為。
本研究使用有限差分法軟體FLAC5.0來模擬人工湖的湖水下滲至地下水之過程，改變不同的土壤初始飽和度及討論標準砂、壤土、粉質壤土等三種不同種類土壤對人工湖附近地表高程變化及對地下水補注量之影響進行探討。結果顯示(1) 力學-滲流耦合分析與純力學分析之比較結果顯示，純粹只考慮湖水重量之影響(純力學析)，對地表之隆起量並無明顯的變化，但將湖水入滲也考慮進去的話(力學-滲流耦合分析)，地表之隆起量有顯著的增加，隆起量增加的原因主要是在濕潤面的推進下，土壤基質吸力的消散、土壤飽和度增加，間接反應在有效應力的降低所導致。(2) 在初始飽和度之參數影響方面，在不同初始飽和度(70%、60%、50%)中，以初始飽和度70%之隆起量為最大、飽和度60%次之、飽和度50%最小，但初始飽和度對最終累積的地下水補注量之影響不大。(3) 比較砂、壤土、粉質壤土隊隆起量與補注量之影響，發現土壤飽和滲透係數越高，其最終累積的地下水補注量越多，但地表最終的隆起量卻較小。所以如果以地下水之補注量為考量時，人工湖應設置於透水性良好之砂土層，但其所回升的地表高程可能就不如細粒料含量較多的土壤。

關鍵字

二相流模式 ； 雙降伏模式 ； 數值分析 ； 人工湖 ； 地下水補注 ； 非飽和土壤

並列摘要

Taiwan is located in subtropical regions. Frequent rainfall often occurs from May to October. However, there is poor rainfall in most areas from November to April. The proportion of digging well to pump groundwater increases because that the spatial and transient distributions of water resources are not uniform. But over-pumping groundwater causes lowering water table and subsurface settlement.
It is an unsaturated analysis to discuss the recharge process of ground water. The two-phase flow was performed to simulate the infiltration behavior of water in ground water recharge problem. Soil medium underwent the process of loading or unloading when water table fell or rose, respectively. The increase of elastic modulus is induced by reducing of pore volume when soil is loading. The mechanical behavior of modulus increase was introduced in the study by using FLAC with double yield model instead of Mohr-Coulomb model.
This study was used FLAC to simulate the infiltration process of water in artificial lake recharge case. A parametric study is also performed. The influences of the kind of soil, including sand, loam and silty loam and initial degree of saturation on ground elevation and the total amount of water by recharged. The results show that the stiffness of soil is volumetric strain independent by using Mohr-Coulomb model, but the soil stiffness depends on volumetric strain of soil by using double yield model. The heave of ground surface increases with increasing initial degree of saturation of soil in groundwater recharging phase. The initial degree of saturation is an insignificant factor on the total amount of recharging ground water. However, the total amount of recharging ground water in sand layer is larger than other soils due to its high permeability. But the heave of ground surface is less in sand layer because of less finer particle content.

並列關鍵字

two-phase Model ； double-yield Model ； numerical analysis ； artificial lake ； groundwater recharge ； unsaturated soil

參考文獻

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