土壤邊坡降雨入滲行為之探討

Analysis of rainfall infiltration in unsaturated soil slopes

呂明杰(Ming-Chieh Lu)

指導教授 ： 馮道偉

中原大學/工學院/土木工程研究所/碩士(2004年)

https://doi.org/10.6840/cycu200400054

摘要

中文摘要

台灣由於平原區域之開發幾乎已達飽和狀態，因此對於擁有許多高山及丘陵地之台灣島而言，坡地的開發更顯重要。由於台灣之海島型氣候，豐水期期間之集中降雨常造成坡地破壞，故本研究之目的在於了解降雨入滲於未飽和邊坡之行為特性。
本研究以數值模擬方式，進行均勻細砂、砂土質壤土、粉土質粘土及龍潭紅土四種未飽和土壤邊坡之降雨入滲分析，藉此探討這四種不同性質土壤於未飽和狀態下之入滲行為，此外對於坡面降雨入滲所造成之影響亦加以探討。均勻細砂、砂土質壤土及粉土質粘土三種土壤為數值分析軟體內建土壤，數值分析時所需之體積含水量函數與水力傳導函數皆已建立於軟體中。而龍潭紅土為現地土樣，所以必須自行推導此兩項函數方能進行數值分析，研究中使用的體積含水量函數推導式為MK- Modified Kovacs推算式，水力傳導函數推導式為Green和Corey推算式。均勻細砂、砂土質壤土、粉土質粘土於分析時使用26.5°、45°、63.4°三種坡度，坡頂降雨範圍為2倍、5倍、10倍坡高距離，降雨強度分別為5、10、20、30、40、50 mm/hr進行分析；龍潭紅土分析時使用與現地坡度相同的45°，坡頂降雨範圍為2倍坡高距離，降雨強度分別為5、10、20、30、40、50 mm/hr進行分析。
分析結果得到以下結論：（1）進行邊坡降雨入滲數值分析時，坡頂降雨範圍取用坡高2倍距離即可；（2）經由地表入滲率及入滲百分比圖可以了解土壤於降雨期間雨水入滲狀況，對於降雨過後浸潤深度之發展有重要影響；（3）當降雨強度大於土壤飽和滲透係數時，由於入滲行為受到飽和滲透係數控制，使得這些降雨強度作用下分析結果完全相同；（4）未飽和土壤邊坡入滲行為受到土壤本身水力傳導函數之影響，當土壤之水力傳導函數於未飽和部份所對應之滲透係數較高，則土壤於未飽和狀態下入滲速度較快，使得影響區域較大，若土壤之水力傳導函數於未飽和部份所對應之滲透係數較低，則結果相反；（5）坡面降雨入滲部份對於土壤之水力傳導函數於未飽和部份所對應之滲透係數較高者影響較大，容易造成坡頂向下滲入水流受到推擠而變化流動方向，形成部份水流向遠離坡面方向流動；（6）滲流速度會隨降雨強度增加而加快，但是當降雨強度大於飽和滲透係數時，不同降雨強度於相同時間點所得到之滲流速度皆相同；（7）使用Lumb浸潤帶推算式推估浸潤深度上與數值分析結果有差異。

關鍵字

邊坡降雨 ； 入滲 ； 未飽和土壤

並列摘要

ABSTRACT

In Taiwan, most of the slope failure happened during the oceanic climate rainfall. The objective of this study is to understand the infiltration behavior of unsaturated slope during rainfall.
This study used four types of soils in numerical analysis, including uniform fine sand, sandy loam, silt clay and Lungtan red soil. The infiltration in unsaturated condition and the effects on the slope had been explored. Among these soils, the uniform fine sand, sandy loam, silt clay have date built-in the numerical analysis software, including the volumetric water content function and the hydraulic conductivity function. The data of the Lungtan red soil needs to be derived. The volumetric water content function is derived by MK-Modified Kovacs method, and the hydraulic conductivity function is derived using the Green and Corey method. In this study, the inclination angles of the uniform fine sand, sandy loam, and silt clay slope are 26.5°, 45° and 63.4°. The rainfall intensities are 5, 10, 20, 30, 40 and 50 mm/hr. The Lungtan red soil slope is inclined at 45°.
The results of this study indicate that: 1) the wetting band could be influenced by the infiltration rate and infiltration ratio; 2) when the rainfall intensity is greater than the saturated hydraulic conductivity, the analysis results are the same; 3) the unsaturated infiltration behavior is related to hydraulic conductivity function; 4) if the rainfall is increased, the infiltration velocity is also increased; 5) Lumb’s wetting band equation for predicting the depth of the infiltration gives very different results from the numerical analysis.

並列關鍵字

rainfall infiltration ； unsaturated soil slopes

參考文獻

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