入滲為水文地質中一項重要之研究課題。現有的入滲模式多以單相流移動來建構理論，未將氣相移動納入考慮。本研究探討入滲過程中，液相於土壤中擠壓孔隙間氣體，形成兩相流動，氣相的移動又擠壓了潮濕鋒前土壤中原有之含水量，使得含水量下降，而後入滲水流抵達造成含水量快速上升。因此，在入滲過程中土壤含水量會有先下降再上升的現象。本研究進行兩相流入滲之理論探討跟實驗操作。在理論部份(1)忽略重力效應(2)忽略毛細效應情況下，採用Buckley and Leverett [1942] 模式計算兩相流體之運移距離與飽和度變化關係。其關係式可用於描述氣流鋒面與水流鋒面之移動，及土壤剖面之含水量變化。本研究中砂箱試驗，進行定水頭實驗，觀察試驗箱三處深度位置之含水量隨時間變化關係。設計三組實驗，每組進行至少三次重覆試驗。最後將理論模式應用於實驗結果，其結果顯示入滲水流受到氣流影響是十分顯著地，兩相流理論可用於描述入滲過程，但模式假設必須進一步移除，方能提高模式量化之精準。

Infiltration is an important component in hydrogeological research. Most of the existing infiltration theories are constructed based on single-phase model for water movement, and those models do not account for the movement of gas phase. This study investigated the infiltration process using two-phase model. The liquid expels air in the soil void to generate the two-phase flow. The air extrudes the initial moisture content in the soil ahead of the wetting front such that the water content decreases. With the wetting front arrived, the water content rapidly increases to reach equilibrium. Therefore, the water content falls at first and rises later in the infiltration process. This study explores the application of two-phase model to the experimental data. In the theoretical part, the fluids are assumed incompressible. The travel distance of fluid migration for given saturation were calculated by Buckley and Leverett [1942] model. The results are used to describe the movement of water front and air front, and also the water content changes of the soil profile. In the sand box experiments, the ponded water head is remained constant. Variation of water content with time at three different depths are recorded. Three experiment sets were design. Each set is performed for three times. The model was applied to the experimental data. The results show that the two-phase infiltration model is applicable to describe the infiltration process. However, the quantitative assessment can be improved by relaxing the assumptions.

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