堰塞湖天然壩在短時間內極有可能發生潰決，所以本研究採用有限元素法（ABAQUS）模擬非飽和天然壩之滲流-漸進式破壞，探討分析滲流-漸進式破壞過程中現象及原因。由模擬結果顯示產生滲流-漸進式破壞的原因是，隨著水位上升，孔隙水壓不斷增加，基質吸力下降導致有效應力的減少，從而使土壤的抗剪強度降低，造成下游坡面的不穩定，若土體因滲流力開始發生破壞，則會不斷往壩頂方向發展，最終導致壩頂高度下降，蓄水溢頂而造成潰決。
ABAQUS模擬之滲出點位、滲流角度及溢流侵蝕時位移趨勢與水工模型試驗進行比較，結果大致相符。由模擬可知，下游坡面滲流角度漸緩的區域流速及水力坡降最大，且滲流角度受下游坡度及渠道坡度影響，本文將滲流角度最小臨界值定義為λ=90°-θd+θt，可結合Budhu and Gobin（1996）的土體滲流破壞機制理論可準確判斷滲出點位、在滲流力作用是否使下游坡面產生破壞及水位變化導致不穩定坡面之範圍。
通過唐家山堰塞湖天然壩為案例進行模擬，結果顯示在水位為743.1m時滲出點位置位於高程681.33m，根據滲流角度判定在下游側高程為708.70m~719.36m的範圍極有可能會發生滲流破壞的情形。

There are wide acknowledgements that the landslide-dam is likely to crack down in a transitory time. Thus, this study uses finite element method (ABAQUS) to simulate the seepage-progressive failure of the unsaturated landslide-dam, by which the author could analyze the phenomenon and causes of such processes. The results of simulation demonstrate that the cause of seepage-progressive failure as follows: as the water level rises, the pore water pressure increases continuously so that the decreases in matric suction, which leads to the decreasing of effective stress and the reduction of shear strength of soil is resulting in instability of the downstream slope. If the soil begins to break down due to the seepage force, it will continue to develop toward the top of the dam, eventually leading to a drop in the height of the crest causing overtopping.

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