不同規格環圈柱於橋墩沖刷保護效果之研究

Abstract

In the west of Taiwan, bed elevations of many rivers lowered down seriously. River and bridge management bureaus often construct bridge protection works around piers to reduce the scouring of the pier foundations. However, the results are still unsatisfactory. In this study, the use of ring columns as a pier protection countermeasure is reported. The ring columns consisting of cylindrical rubber rings are placed upstream of a bridge pier to reduce the flow impacting energy and scour by its’ irregular surface roughness and porous characteristics. A series of experiment was conducted with uniform sediments under the clear-water steady flow (V/Vc<1) conditions. By changing the ring specifications, and distances between ring columns and the pier in order to understand the scour depth reduction effect and propose an optimal allocation of protection works. The results show that, when the ring specifications and the ring columns to set the distance change, the range of influence on the flow generated will be changed, resulting in different energy dissipation. In general, when the ring presents Type III (DR=0.28/b) with the diameter D/b=0.8, ring columns protection appear the best protection effect at the distance L/b=4, and pier scour depth reduction rate by 30.3%.

台灣西部許多河川河床嚴重下降，河川及橋樑管理單位經常於橋墩周圍構築保護工，以減少墩基礎之沖刷惟其效果有限。因此本研究研發新型橋墩基礎保護工法—透水性環圈柱，此工法乃使用具有彈性的橡皮環圈組成具透水性之類圓柱體，設置於橋墩上游，利用其不規則表面糙度及多孔隙透水特性以削弱水流對橋墩的衝擊能量。本研究透過水工試驗模擬在定量清水流(V/Vc<1)條件下，探討不同環圈規格在不同環圈柱設置距離之沖刷減緩效果，以獲致較佳之橋墩保護工配置模式。 研究結果顯示，當環圈規格與環圈柱設置距離改變時，保護工對水流產生的影響範圍會隨之化，造成不同的消能效果。整體而言，當環圈規格為III 型(DR/b=0.28)組成之直徑D/b=0.8，環圈柱保護工設置距離以L/b=4 之保護效果為最佳，沖刷減緩率為30.3%。