變量流橋墩沖刷保護工之試驗分析

Analysis of Countermeasures to Protect Pier Scour Evolution Unsteady Flow Condition

潘思羽(Siu-Yu Pan)

指導教授 ： 李政賢

淡江大學/工學院/水資源及環境工程學系碩士班/碩士(2018年)

https://doi.org/10.6846/TKU.2018.00126

摘要

橋墩為重要交通建設，長年於河道或水路中受水流沖刷，過度沖刷會造成橋墩地基破壞，因此如何保護橋墩不受沖刷破壞為橋上安全的重要問題。橋墩周圍局部沖刷主要受到向下水流、馬蹄形渦流及尾跡渦流作用影響。
本研究利用三種不同橋墩保護工，在循環水槽下模擬變量流，探討沖刷深度的變化。試驗設計兩組變量流，包括中峰型與前峰型變量流歷線，搭配三種不同保護工，分別有犧牲樁、螺紋及淹沒葉片保護工，在均勻顆粒下，針對犧牲樁數目、螺紋直徑及厚度還有淹沒葉片厚度不同參數條件，利用探針紀錄橋墩前方沖刷深度歷程及沖刷地形，分析不同橋墩保護工對於沖刷深度影響，得到最佳橋墩保護工配置模式。
研究結果顯示，在淹沒葉片及螺紋保護工下，在沖刷剛開始0~30分鐘內，其減少效率約為50%，不過30分鐘後，甚至出現比無防護橋墩下更深的深度，這兩種保護工保護效果不佳; 但在犧牲樁保護工下，發現沖刷時間30~60分鐘內，樁後有沙丘形成，可明顯降低沖刷深度，此時效率可高達50%以上，且在五根犧牲樁保護下時，出現超過100%的減少效率，而平均效率也有40%左右，是三保護工中效率最顯著保護工。

關鍵字

橋墩沖刷 ； 變量流 ； 保護工

並列摘要

Pier scouring can cause damage of hydraulic construction, so protecting piers against scour is an important issue in bridge construction. In the study, a series of experiments were conducted under the unsteady flow conditions to evaluate the effectiveness of different countermeasures protection arrangements for protecting the pier. Both central peak and advanced peak hydrographs were adopted and uniform sediment was used. Sacrificial piles, threaded pile, and submerged vanes were adopted. This study considered various parameter, including (1)numbers of piles, (2)threaded pile diameter and thickness, and (3)vane thickness. Temporal evolutions of pier scour are recorded by using a probe. The results show that the efficiency of submerged vanes and threaded pile are less than 50% within 30 minutes; however, after 30 minutes, the scour depth with protection exceeds that without protection. The countermeasures of submerged vanes and threaded pile do not perform well, compared to sacrificial piles. The average efficiency of sacrificial piles up to 40%, and the maximum efficiency of five sacrificial piles can exceed 100%. Consequently, sacrificial piles have the most significant efficiency in the three countermeasures.

並列關鍵字

Pier scour ； Unsteady flow ； Countermeasures

參考文獻

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