Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/14106
標題: 變量流流況下非均勻圓柱型橋墩局部沖刷之研究
Local Scour around Nonuniform Circular Piers under Unsteady Flow
作者: 鄭暐曦
Cheng, Wei Shi
關鍵字: Local Scour;變量流;Unsteady Flow;Pier;非均勻橋墩;局部沖刷
出版社: 土木工程學系
摘要: 
橋墩基礎裸露為台灣橋樑目前面臨之主要問題之一。河川常因人為或天然因素而發生一般沖淤,橋墩基礎之阻水面積較大,則易產生局部沖刷,兩者均可能影響橋樑安全。
目前一般均採用拋石、蛇籠或包墩做為橋樑基礎之保護方式,惟若設計規劃不當,將降低橋墩間之通水面積,進而產生束縮沖刷,並加速橋墩處之局部沖刷。因此,非均勻橋墩(即圓柱型橋墩位於圓柱型基礎之上)之沖刷特性與不均勻面處之沖刷機制應加以深入研究,以利最佳保護工法之研擬。
本研究針對清水沖刷之情況下,以較接近天然情況之變量流流況,包括前、中、後峯流量歷線,配合非均勻橋墩,進行室內試驗模擬,研究中並探討覆土面位於橋墩不均勻面之上(橋墩基礎未裸露),以及橋墩不均勻面之下(橋墩基礎裸露),所造成局部沖刷之差異。
試驗結果顯示,在相同水流條件下,覆土面位於橋墩不均勻面之上時之沖刷深度,較位於橋墩不均勻面之下時低,即前者可有效降低橋墩前緣沖刷深度。主要為橋墩與基礎間之不均勻面,可有效降低下降流強度,並增加沖刷坑擴大之時間。依本試驗結果,兩者所造成沖刷深度之降低量,以中峯型態之流量歷線為最大。

One of the major problems relating to the bridge damage in Taiwan is the exposure of the bridge foundations. General scour may occur in a river due to either the man-induced or natural causes. Local scour is attributable to the existence of the bridge. Both general and local scours may affect the safety of a bridge.
In this study, different types of unsteady flow hydrographs, including the advanced, symmetrical, and delayed hydrographs, with non-uniform piers were used to conduct the laboratory bridge scouring experiments. The variation of local scour depth with exposure elevation (i.e. the relative elevation between the channel bed elevation and the discontinuous surface of non-uniform pier) was also investigated.
The experimental results revealed that the scour depth for the case with the soil surface above the discontinuous surface (foundation not exposed) was smaller than the case with the foundation exposed. The results implied that the discontinuous surface of the non-uniform pier can effectively reduce the local scour depth. In addition, it was found that among three kinds of hydrographs, maximum amount of reduction on the local scour occurred for the symmetrical flow hydrograph.
URI: http://hdl.handle.net/11455/14106
Appears in Collections:土木工程學系所

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