山洪濁流形成沖積扇之實驗研究;Experiment study of alluvial fans formed by torrential floods

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Title:	山洪濁流形成沖積扇之實驗研究;Experiment study of alluvial fans formed by torrential floods
Authors:	吳俊銓;Wu,Chun-chuan
Contributors:	土木工程研究所
Keywords:	前積層;沖積扇;頂積層;顆粒濃度;質點影像測速法;Sediment Concentration;Topset;Foreset;Alluvial Fan;PIV(Particle Image Velocimetry)
Date:	2012-07-25
Issue Date:	2012-09-11 18:04:17 (UTC+8)
Publisher:	國立中央大學
Abstract:	高降雨強度及高降雨延時事件帶來山洪及相伴而生之岩屑崩滑、坡體失穩、土石流及洪流等事件，對居民及交通建設造成災害損失甚鉅。台灣東澳台九線 115.9K 及 116.1K 於 2010 年受梅姬颱風強降雨影響，引發土石流直接溢淹蘇花公路至太平洋海岸線而形成沖積扇(alluvial fan)，本研究以此案例探討山洪濁流形成沖積扇之動態過程與堆積機制。本研究進行小尺度二維渠槽實驗，搭配高速攝影機，對顆粒流堆積歷程、前積層(foreset)及頂積層(topset)堆積角度、水深及流動層速度分佈作分析與討論。並使用不同顆粒粒徑(D)、水入流量(Q w )及顆粒入流量(Q s )作為實驗主要控制因素，後兩項之比值為本研究重要的無因次參數，初始水砂排放比(n 0 )；而藉由簡單推算頂積層顆粒流量得到實際水砂排放比(n)，以此無因次參數探討頂積層坡度變化關係，研究結果顯示頂積層坡度與水砂排放比成反比關係。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，在自由水面等同或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；而自由水面高於顆粒流表面許多時，流動層底部仍遵循 SSH 之指數分佈，但流動層頂部接近自由表面處受水流影響甚鉅，速度分佈較遵循 Bagnold 流變特性。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 progress of granular flows, deposit angle of foreset and topset, and flow patterns with a high-speed camera. Theparticle size (D), water discharge (Q w ), and sediment discharge (Q s ) dominates the flow patterns, and the slopes of foreset and topset mainly depend on sediment concentration (i.e., the ratio of sediment discharge to water discharge).The slope of topset increases with increasing sediment concentration. 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 equal to or slightly higher than granular-flow surface. When the free surface is substantially higher than granular-flow surface, the lower part of the velocity profile in the flowing layer still obey SSH rheology. The upper part of velocity profiles near the free surface follow the Bagnold-type velocity profiles instead.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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