為預測降雨導致邊坡產生連續滑動或土石流，本研究先以一底部為剛性不透水的模型砂槽，採用南投北港溪粉土質細砂（統一土壤分類：SM）建立一深0.32m、寬1.35m、高0.7m，坡角與水平呈30°的砂質邊坡，進行一系列的模擬降雨試驗。試驗中量測邊坡內部含水量分佈與土砂流出量，以探討不透水岩盤上之砂質邊坡，在豪雨中邊坡後退式破壞的機制。
研究發現砂質邊坡土壤顆粒的排出主要是坡趾液化後，土壤顆粒被水流帶出的結果，而坡趾液化則是因邊坡內部滲流水沿著土壤和底岩界面流出產生。在本研究中所獲得之土體流失曲線中有一反曲點，此反曲點可代表坡趾從輕微破壞轉變為急劇的後退式破壞。在研究中亦發現當邊坡土粒流出量達到邊坡土粒總固體體積之3%~5%時，且此一發生時間與土岩界面處達到飽和時間有密切關係，因此設置於土－岩交界面之水份計達到飽和之時間，可作為坡趾破壞及後續後退式破壞之早期預警。
在以上試驗過程觀察邊坡破壞的現象後，為進一步由數值分析探討邊坡因降雨滲流導致破壞的機制，繼之進行土壤飽和滲透係數、未飽和土壤剪力強度、土壤水分特性曲線相關試驗與分析，以獲得邊坡降雨數值模擬所需之參數。在由定水頭透水試驗求取土壤飽和滲透係數與孔隙比關係中，發現飽和滲透係數隨孔隙比增加而增大，而飽和滲透係數與孔隙比的平方也約略呈線性關係增加。換言之，土壤愈疏鬆，雨水滲入速度將愈快。而未飽和土壤剪力強度則利用長、寬各為15cm，上下盒深度各為5cm之直剪儀進行不同孔隙比及不同含水量之一系列未飽和土壤直剪試驗，發現未飽和土壤摩擦角φ受孔隙比影響較大，而在相同孔隙比下，土壤摩擦角φ受含水量變化之影響則不明顯。而土壤水分特性曲線則利用砂箱中埋置張力計與水分計，於濕潤及乾燥過程中記錄水分計與張力計讀數之相對關係，繪出試驗用土壤之水分特性曲線，再由水分特性曲線推導土壤之水力傳導函數。本研究在有限元素分析程式SEEP/W中採用上述試驗所得土壤參數，進行砂箱垂直滲流及降雨對邊坡土體內部含水量變化過程之分析，獲得與試驗過程相當吻合之分析結果，對降雨造成邊坡破壞機制理論模式建立良好之發展基礎。

A series of rainfall tests on 0.32 m-deep, 0.7 m–high, 1.35 m–wide sandy slopes resting on an impermeable rigid base inclined at 30° from the horizontal was performed to predict of rainfall-induced flow-slides and / or debris flows. In-soil moisture content and solid discharge measurements were performed to gain insights into the rainfall-induced retrogressive slope failure. The solid (or debris) discharge was a result of the wash-out of the fluidized slope toe by the interflow along the soil-bedrock interface. In this study the mass wasting curves have inflection points representing transitions from minor toe failures into remarkable retrogressive failures. At the first inflection point of the Qs vs. t curve and 5% of total solid volume discharge, values of Sr at a certain distance from the toe for the soil-bedrock interface were higher than those measured at the same distance from the toe for the 0.2 m-below-surface zone, indicating the effect of infiltration-induced interflow along the soil-bedrock interface and its effect on the fluidization of the slope toe and the retrogressive failure of the slope.
Observe the slope failure in the above process of the test, discuss the mechanism of slope failure of rainfall-induced further, this study carried on the saturated permeability coefficient, the shear strength of unsaturated soil, soil-water characteristic curves correlated with testing and analyzing. To obtain the relationship between the saturated permeability coefficient and void ratio from the constant head permeability test, gained if the void ratio is increased, the saturated permeability coefficient is also increased. In the same void ratio, the angle of internal friction varied is unapparent for various water content.
This study used these soil parameters while being above-mentioned to apply with SEEP/W program by procedure, it obtain to be quite identical simulation result with process of the test, this is a basis of distinction for analysing slope seepage and slope stability future.

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