應用二維水理輸砂模式於橋墩沖刷之模擬分析探討

Using 2-D Numerical Model Simulation on Bridge Scouring

李豐佐(Fong-Zuo Lee) ； 黃聰憲(Tsung-Hsien Huang) ； 賴進松(Jihn-Sung Lai) ； 林詠彬(Yung-Bin Lin) ； 張國鎮(Kuo-Chun Chang)

《農業工程學報》 63卷4期 (2017/12) Pp. 65-78

https://doi.org/10.29974/JTAE.201712_63(4).0005

摘要

2009年莫拉克颱風期間造成橋台、橋墩、橋面板或引道等損毀之橋梁共有上百座，除了橋梁因設計年限之安全結構問題，其原因乃在颱洪期間橋梁所在之河道底床受到洪水沖蝕而刷深。本研究以推估橋梁墩前最大橋墩沖刷深度為主，區域為大甲溪國道三號橋，研究範圍介於大斷面編號13至編號7之間，所涵蓋區域長約3,285m，寬約1,165m，主要分析位置為編號P28L橋墩。本研究採用SRH-2D二維水理輸砂模式執行動床水理運算，搭配Parker (1990)泥砂傳輸公式計算一般沖刷深度，再利用水理動床運算結果所獲得之水文參數以Inglis (1949)公式、Laursen (1958)公式、Neill (1964)公式、Shen et al. (1966)公式、吳建民(1967)公式、Jain and Fischer(1980)公式及Froehlich (1991)公式等七種進行局部沖刷計算，以及Laursen (1958)公式計算束縮沖刷深度。根據國家地震工程研究中心於P28L 所安裝之沖刷深度監測感應器，以2014年0519豪雨事件作為模擬條件，考量墩前不同距離計算沖刷深度，分析水流與橋墩夾角0°、15°、30°、45°等多種角度推估地形及水位之關係，發現沿橋墩上游面所造成之墩前壅水影響水平範圍大約為10m。在各種來流方向角度的沖刷深推估後所獲得之結果均相當接近，因此最後仍建議以墩前0°及五倍橋墩直徑距離上游處的來流水深及流速，作為橋梁最大沖刷深度之推估位置，且以Froehlich(1991)公式所推估之沖刷深度結果，較接近現場實際觀測値。然而，因各河川河道輸砂特性各異、橋墩形式與尺寸、水文水理條件也不盡相同，本研究僅針對單一河川區段進行研究，且以大甲溪國道三號橋為本研究之案例，因此，未來應針對各重要橋梁分別進行橋梁沖刷深度推估，以作為橋梁安全評估參考之用。

關鍵字

橋墩沖刷 ； 二維數值模式 ； 局部沖刷 ； 束縮沖刷 ； 一般沖刷

並列摘要

Hundreds of bridges of abutments, piers, deck and approach roads damaged during Typhoon Morakot in 2009. Except the structural security problems due to the service life, the river bed where the bridge located were scoured deeply by flood is the main reason. In this study, estimating the largest scour depth of front of the bridge is the purpose. The analyzing pier named PL28, located at National Freeway Bridge in the Dajia River, the reach is about 3,285 m long and 1,165 m wide between the cross section 7 and cross section 13. A 2-D numerical model, SRH-2D, is adapted to simulate hydraulic mechanism and sediment transport in study area. The general scour depth is calculated by Parker's equation which is one of equations of sediment transport simulations in SRH-2D. Furthermore, the simulated results of hydraulic patterns can be adapted to calculate the local scour depth by the Inglis formula, Laursen formula, Neill formula, Shen et al. formula, Wu formula, Jain and Fischer formula and Froehlich formula etc. Then, the contraction scour depth which is calculated by Laursen's equation is integrated with general scour depth and local scour depth to complete total scour depth. The final results were compared to the monitoring sensors installed by the National Center for Research on Earthquake Engineering in Taiwan. One rainfall event named 0519 (2014) was selected to be the event in the simulation and the field case. In this study, not only calculating the scour depth in the front of bridge, but also designed four kinds of angles 0°, 15°, 30°, 45° which are between the water and pier to estimate the relationship between bed element and water level. We found that the horizontal influence distance of backwater resulted from the pier is about 10 m. In addition, the scour depths estimated in various angles are quite closed. Therefore, it is recommended to use the 0° and the five times diameter of the pier as the position to estimate the total bridge scour depth. Based on comparison results, the Froehlich formula is recommend being the estimation formula in this research area after comparing with the estimating and measuring data. However, due to the different characteristics and the hydrological conditions are not the same of each river, the results of this study only proposed for the National Highway No. 3 Bridge pier in the Daija River. It is suggested to continue study on the bridge scour depth in all important bridges. Thus, the specific suitable formula on allocated bridge scour estimation could be obtained, and the bridge project safety could be assessed.

並列關鍵字

Bridge scour ； 2-D numerical model ； local scour ； contraction scour ； general scour