防砂壩在河川及集水區治理上，扮演著非常重要之角色，它一方面能約束流心減少側岸侵蝕，也能降低河道縱坡減少河床沖刷，穩定兩岸山腹，是傳統以來治山防洪常用的手段，亦是土石流攔阻工程中最常使用的工法之一，且建造位置大多位於野溪中、上游處，所建造的型式大多採封閉式或開放式的直立型與斜面型重力式防砂壩為主，但經由現地調查發現防砂壩在攔阻土石流時，壩體因所受土石流衝擊力量強大，常有毀損情況發生，因此需對防砂壩的型式重新檢討。目前防砂壩之設計也因施工方法的進步，漸漸的朝向較經濟(所用材料較省)、較穩定(所受力量較小)之方向去評估比較。本文構想朝藉由改變壩體上游壩面之幾何形狀，使得土石流作用於壩體之衝擊時間增加以減少受力，並能分散部份土石流衝擊力，增加壩體之穩定性，以期提供未來土石流防砂壩設計之參考依據。因此本文分別以實驗研究及數值模擬研究兩種方式探討防砂壩幾何型式對土石流衝擊力與衝擊過程的影響，以及囚砂率的變化。
由土石流對防砂壩衝擊過程之實驗結果顯示，土石流對壩體衝擊力大小深受壩體幾何形狀的影響，斜面與曲面壩因壩面路徑較直立壩長，使得土石流在壩體上作用時間變長，加上斜面壩斜面出流角度及曲面壩曲面曲率的變化，使得撞擊時流體延渠道方向之動量變化較直立壩小，因此斜面與曲面壩整體受力皆較直立壩小。在實驗結果分析方面，三種壩體於不同實驗條件下衝擊力實測值與理論值均有不錯的相關性，因此本研究所推得之三種壩體受力理論式可描述實驗的結果。
在模擬結果分析方面，壩體受土石流衝擊初期以動壓力為主、靜壓力為輔，之後漸漸地受到回水消能的影響，使得壩前流體流速減緩而逐漸以靜壓力為主、動壓力為輔，最後等到水面趨於平穩時，此時壩體僅受靜壓力作用。總力比較方面，直立壩所受總力為最大，斜面壩次之，曲面壩為最小；動壓力比較方面，直立壩所受動壓力為最大，斜面壩次之，曲面壩為最小；土石流動壓作用的持續時間比較方面，直立壩因回水情況最早發生且回水量最大，因此受土石流動壓作用的持續時間為最短，曲面壩次之，斜面壩為最長；靜壓力比較方面，直立壩因回水量最大，因此所受靜壓力為最大，曲面壩次之，斜面壩為最小；而回水量越多，則囚砂率相對也越高，因此囚砂率以直立壩為最高，曲面壩其次，斜面壩為最低。
實驗與模擬結果顯示，壩體所受土石流衝擊力之大小深受幾何形狀的影響，曲面壩因壩面呈弧形的特性，使得土石流流經路徑為最長且具曲率變化，因此當土石流衝擊壩體時，除使土石流作用於壩體之衝擊時間增加以減少受力，並能夠藉由曲率的變化分散部份衝擊力，因此所受之土石流衝擊力較其他兩種壩體小。

For river and basin management, it is important to construct Sabo dams in rivers since they can restrict the channel center line, reduce river bank erosion, and secure hillsides. As such, they are a common method for mountain management and flood disaster prevention. Although Sabo dams are an efficient method for river and basin management, such dams are hit and often damaged by great impulsive force when they block the debris flow. This study analyzed the impulsive force of debris flow on sabo dams with different geometric shapes in order to identify the optimal design for reducing the impulsive force, enhancing stability and minimizing the use of concrete. Therefore, alternative shapes for Sabo dam deserve thorough investigation. In this investigation, a curved dam was designed by changing the upstream-dam-surface geometric shape to reduce the impulsive force of the debris flow, with enhanced stability and reduced concrete mass being the anticipated outcomes.
In this study, the flume and laboratory facilities simulated the impulsive force of the debris flow to the Sabo dams. Three geometric forms, including vertical, slanted and curved Sabo dams, were used to determine the impulsive force. Impulsive force theories of the debris flow were derived from the continuity equation, the momentum equation and the Bernoulli equation. In these, the impulsive force was balanced by the friction force of the Sabo dam and the opposite force of the load cell behind the dam as it was hit by the debris flow. Positive correlations were found when comparing the experimental data with the theoretical results. These findings suggest that the impulsive force theory has predictive validity with regard to the experimental data. This study also presents a three dimensional computational fluid dynamics model using the commercial software FLUENT and FLOW-3D to simulate the impulsive force of debris flow on sabo dams. The simulation revealed the velocity field, distribution of pressure on the dam surface and the forces exerted on the body of the dam.
Based on the experimental and simulation results, the impact geometry has a significant effect on the impulsive force. The time duration of the impact on the dam is longer, and the force impacted on the dam is less. The results clearly show that curved dams exert relatively less force when discharge is large because their arc-shaped dam surfaces produce a long and meandering path of debris flow. Thus, curved dams not only deflect the flow of debris into the dam body, they also lengthen the period of impact, which disperses the impulsive force by means of its changing curvature. Hence, the curved dam exhibits less debris flow-induced impulsive force than the other two designs.

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