本研究利用試體為南投縣眉溪中上游之河砂與地工合成物進行乾砂界面直接剪力試驗，試體尺寸為長300mm、寬300mm、高100mm，在不同單位重及圍壓下，進行乾砂界面靜態直接剪力試驗與乾砂界面反覆直接剪力試驗，從而得到各實驗之剪應力與水平位移量關係等數據，再根據實驗數據求取兩模型(修正R-O模型、修正H-D模型)所需之參數代入公式，並依此公式建立模型以預測土壤之乾砂界面反覆剪動行為，再與先前所作之實驗數據繪圖作比較，評估其符合程度。
本研究根據實驗結果與模型預測結果得知：一、相同圍壓下，尖峰剪應力會隨著單位重增加而增加，其所對應之水平位移量隨著單位重增加而減少；相同單位重時，尖峰剪應力會隨著圍壓的增加而增加，其所對應之水平位移量也隨圍壓增加而增加。二、乾砂界面反覆直接剪力試驗結果顯示，土壤初始剪動時會有硬化情形，但剪動到某個程度時，試體不再隨著剪動而硬化，而是呈現穩定狀態(剪應力維持定值)。三、修正R-O模型在試體尖峰至殘餘狀態之預測，因土壤剪應力不再持續上升故模型預測值與實驗值產生差異。四、修正H-D模型為根據雙曲線理論提出，在試體剪動到殘餘狀態之預測符合程度佳。

To model the relationship between cyclic shear stresses and shear displacements on the soil-geotextile interface, a medium-scale direct shear test apparatus is uesd. The direct shear tests include monotonic sand-geotextile interface tests and cyclic sand-geotextile interface tests using a poorly graded river sand and a nonwoven heat-bonded geotextile.
To simulate the behavior of sand-geotextile interface subjected to cyclic shear loads, the modified Ramberg-Osgood (R-O) model and the modified Hardin-Drnevich (H-D) model are used. Curve fitting from experiment data were carried out to determine model parameters, and the model-predicted stress displacement relationships are compared with the experimental ones.
Results of a comparative study on the stress-displacement relationships between sands and sand-geotextile interface indicate that shear displacements at peak stress states are generally smaller in the case of sand-geotextile interface than that for sands. Since the modified R-O model is an exponential function and H-D ones is a hyperbolic function, the modified H-D model satisfactorily simulates the behavior of sand subjected to large cyclic displacements.

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