Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/98640
標題: Prevention of Bridge Scour with Multi-layer Non-uniform Circular Piers Plane under Unsteady Flows
變量流流況下多層次非均勻橋墩於橋墩沖刷防治之研究
作者: Chuan-Yi Wang
Yan-Ling Lin
Kun-Hao Ciou
Chun-Ming Chang
王傳益
林彥伶
邱琨皓
張峻銘
關鍵字: multi-layer non-uniform piers
unsteady flow
the scouring retardation efficiently
sensitivity analysis
多層次非均勻橋墩
變量流
沖刷減緩效果
敏感度分析
摘要: This study uses hydraulic models to measure the variation of local scour depth with time for multi-layer non-uniform pier (the ratio of the diamete 𝐷/𝐷∗of the upper and middle layers to the pier foundation is 0.4 and 0.7 respectively), and different initial bed level relative to the foundation top elevation (initial bed higher than the upper layer, level with the upper layer, level with the lower layer) under unsteady flows. The research results show that the scour depth increases with an increase flow intensity( 𝑉⁄ 𝑉𝑐=0.5~0.95) under different types of unsteady flow hydrographs. Local scour of the pier occurs in the rising phase of the unsteady flow hydrographs, and the maximum scouring depth occurs after the maximum peak hydrograph. The types of unsteady flow only affects the time of the occurrence of the maximum scouring depth, but has a limited influence on the maximum scouring depth. According to the sensitivity analysis results, the arrival time of peak flow is the most sensitive, followed by the ratio of the height of the middle pier to the pier diameter of the pier foundation( 𝐻 ⁄ 𝐷*), and the lowest is the initial bed level relative to the foundation top elevation. Under the flow conditions of different unsteady flows, when the pier foundation of the multi-layer non-uniform pier is un-exposed (initial bed level higher than the upper layer 10 mm), and the pier height / diameter ratio is 0.4 ( 𝐻 ⁄ 𝐷* ), since the cover bed layer can effectively protect the pier, and the scouring depth can be retarded by the two non-uniform planes of pier, its pier scouring retardation efficiently is the best among the multi-layer non-uniform piers. Opposite results are found for the exposed bridge foundation, because the middle layer of the pier is completely exposed. Considering the safety of bridge structure, a non-uniform circular pier with 𝐻 ⁄ 𝐷*= 0 (two layers) and the un-exposed bridge foundation (initial bed higher than the upper layer 10 mm), its pier scouring retardation efficiently is better than the best of the multi-layer non-uniform piers, so it is the most ideal pier configuration.
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流況作用下,多層次非均勻橋墩(上、中 層墩徑與橋墩基礎之墩徑比分別為𝐷 ⁄𝐷∗ =0.4 及 0.7)於不同覆土高度(覆土高於上層 10 mm、齊平上層及齊 平下層)時,橋墩局部沖刷深度及歷程之變化。研究結果顯示,在不同形式的變量流流況下,沖刷深度會 隨著相對水流強度(𝑉⁄ 𝑉𝑐 =0.5~0.95)增加而增大,橋墩局部沖刷於漲水段發生,且在洪峰到達後達到最大 沖刷深度。不同流況變量流僅影響最大沖刷深度發生時間的早晚,而對最大沖刷深度之大小影響有限。 就敏感度分析結果顯示,洪峰到達時間最為敏感,其次為墩高比𝐻 ⁄ 𝐷 ∗ (基礎墩徑與中層橋墩高度之比值), 最低則為覆土高度。 在不同變量流流況下,多層次橋墩之橋基未裸露時(高於上層 10 mm),且墩高比𝐻 ⁄ 𝐷 ∗ = 0.4,由於覆 土層能有效保護橋墩,且二個不均勻面能有效阻擋向下射流,故其橋墩沖刷減緩效果為多層次橋墩中之 最佳者。而當橋基裸露(齊平下層)時則反之,因橋墩完全裸露所致。考量橋墩水理安全,本研究中於橋墩 墩高比𝐻 ⁄𝐷∗ =0 (雙層),橋基未裸露(覆土高度高於上層 10 mm)時,其橋墩沖刷減緩效果較多層次橋墩中 之最佳者為佳,為最理想之橋墩配置模式。
URI: http://hdl.handle.net/11455/98640
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