臺灣博碩士論文加值系統

本研究主要利用水工模型試驗，模擬近似天然流況之變量流（前峰型、中峰型及後峰型歷線）作用下，不均勻橋墩墩墩徑比( =0.4及0.7)於不同的覆土高度( )時，橋墩局部沖刷深度及歷程之變化。
研究結果顯示，於不同型式變量流歷線作用下，沖刷深度會隨水流強度的增加而增加，同時最大沖刷深度於變量流歷線之上升段完成。中峰型歷線及後峰型歷線之沖刷歷程類似，其最大沖刷深度相當且均高於前峰型，兩者僅有時間稽延之差異。
在各種不同流量歷線作用下，當橋基未裸露( )時，由於不均勻面能夠有效阻擋刷深情況，使得所產生之沖刷深度較小，而橋基裸露( )時則反之。當覆土高度遠高於不均勻面之高度時( )，由於最大沖刷深度未達不均勻面，不均勻面並無減緩沖刷深度之作用，致使沖刷深度反而增加，惟該值仍低於橋基裸露之情況。
而在不均勻橋墩墩徑比( )不同時， =0.4之局部沖刷深度皆低於 =0.7，且前者之沖刷坑體積減緩效果明顯優於後者，其中又以 =0.6之沖刷坑體積減緩率效果最佳。在考量橋墩水理安全之情況下， =0.4為較理想之不均勻橋墩型式。

This study uses hydraulic models to measure the variation of local scour depth with time for non-uniform pier diameter ratios of 0.4 and 0.7, and different initial bed level relative to the foundation top elevation under unsteady flows with advanced, central and delayed peaks.
The research results show that the scour depth increases with an increase of flow intensity under different types of unsteady flow hydrographs. The scour depth reaches a maximum value within the rising phase of the unsteady flow. The scour variation for the central peak hydrograph is similar to that for the delayed peak hydrograph, and both of their scour depths are greater than that for the advanced peak hydrograph. The only discrepancy for the first two curves is the time lag.
Because of the scouring retardation by the top of foundation, the scour depth is reduced for the un-exposed bridge foundation ( ) under any unsteady flow. Opposite results are found for the exposed bridge foundation ( ). When the distance between the top of foundation and the initial bed level is greater than the scour depth ( ), the foundation top cannot retard scouring efficiently which leads scour depth to increase. However, the scour depth is still less than the condition with the bridge foundation exposed initially.
As regards to the effect of non-uniform pier diameter ratio ( ), local scour depth for a ratio of 0.4 is less than that for a ratio of 0.7. Also the former is more effective in scour hole volume retardation than the latter. The most effective scour hole volume retardation occurs when equals 0.6. Considering the safety of bridge structure, a non-uniform pier with equals to 0.4 is an ideal pier style.

目 錄
頁 次
謝誌 I

摘要 II

目錄 IV

圖目錄 VII

表目錄 X

照片目錄 XI

附圖目錄 XII

符號表 XIII


壹、前言 1
1.1 研究動機 1
1.2 研究目的 2
1.3內容組織 3
貳、文獻回顧 4
2.1均勻橋墩沖刷 5
2.2不均勻橋墩沖刷 7
2.3等效橋墩 10
2.4橋墩周圍局部沖刷特性 12
2.5影響橋墩沖刷因子 14
參、理論分析 24
3.1圓柱型橋墩周圍水流之流況 24
3.2橋墩周圍局部沖刷之過程 26
3.3沿壁沖射流理論 28
3.4渦流理論 34
3.5因次分析 37
肆、水工模型試驗 41
4.1模型與原型之比例關係 41
4.2試驗設備與佈置 42
4.2.1試驗渠槽 42
4.2.2試驗橋墩模型 43
4.2.3試驗佈置 44
4.2.4試驗儀器 45
4.3試驗河床質 46
4.4試驗流量 47
4.5完全發展段 49
4.6渠槽試驗條件 50
4.7試驗步驟 51
4.7.1試驗橋墩安置與底床質鋪設 51
4.7.2試驗流量控制 51
4.7.3沖刷深度與河床剖面量測 52
4.7.4試驗操作程序 52
伍、結果分析與討論 54
5.1一般沖刷、束縮沖刷與局部沖刷之分離 54
5.2沖刷坑與淤積堆之縱斷面變化 55
5.3沖刷坑之長度( )與寬度( )探討
61
5.4流量歷線對沖刷深度之影響 63
5.5橋墩不均勻面位置對沖刷深度之影響 66
5.6不均勻橋墩徑墩比( )對沖刷深度之影響
70
5.7局部沖刷坑體積之變化 71
5.8本研究與Melville(1996)沖刷深度之比較 73
陸、結論與建議 75
6.1結論 75
6.2建議 77
參考文獻 79

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