高降雨強度事件帶來山洪及相伴而生之坡體滑動、土石流及洪流等事件，對民眾及交通設施造成嚴重災害損失甚大。台灣東澳台九線在2010 年10月受梅姬颱風影響，引發土石流直接掩埋蘇花公路至太平洋海岸線而形成沖積扇(alluvial fan)，本研究探討土石流形成沖積扇之動態過程與堆積機制，並在前人的研究上探討向源回堵發生的情形與發生機制。本研究進行小尺度渠槽實驗，搭配相機與高速攝影機，對顆粒流堆積歷程、堆積角度、水深、滲流和流動層速度作分析與探討。以不同顆粒粒徑(D)、水入流量(Qw) 、顆粒入流量(Qs)及渠床長度(L)作為實驗主要控制因素，水流量與顆粒入流量之比值，即水砂排放比(n)為本研究重要的無因次參數。由水砂排放比來研究回堵發生的機制與坡度變化的關係，研究結果顯示堆積坡度與水砂排放比成反比關係，且在某個臨界值之後，坡度會劇烈爬升。本研究使用質點影像測速法(Particle Image Velocimetry, PIV)探討顆粒流動層速度分佈情形。研究結果顯示，在水位線略高於顆粒流表面時，受邊壁效應(wall effect)影響，流動層速度剖面遵循超穩態流變學(super-stable heap rheology, SSH)之指數分佈；而水位線等於顆粒流表面時，速度剖面呈現一趨近於線性的流速分布，水位線低於顆粒表面時，上層顆粒無法被水推動，只受重力的影響往下游運移，流速分布則較無明確趨勢。

Mountain floods accompanied with landslides, slope avalanches and debris flows often cause tremendous disasters to downstream residents and infrastructures. The dynamic process and deposit mechanism of alluvial fans by torrential flows is experimentally explored in this study. An acrylic flume experiment is adopted to observe the deposit process of granular flows, deposit angle of topset, infiltration of granular ,and flow patterns with a high-speed camera. The particle size (D), water discharge (Qw), granular discharge (Qs) , and bed length(L) dominates the flow patterns, and the slopes of topset mainly depend on the ratio of granular discharge to water discharge.The slope of topset increases with increasing sediment concentration ,but increasing abruptly exceeding a specific value. The velocity profiles of the flowing layer are explored by using particle image velocimetry (PIV). The velocity profiles in the flowing layer depict SSH rheology when the free surface is substantially higher than granular-flow surface. When the free surface is substantially equal to granular-flow surface, the velocity profiles approximates linear.

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