橋梁沖刷監測預警系統建置之試驗研究

Abstract

台灣因河流密布、地形破碎，跨河橋梁在交通路網中扮演非常重要之角色，而跨河橋梁普遍存在各種沖刷受災現象，隨全球氣候變遷，颱風及豪雨帶來之雨量及造成的危害一再突破歷史記錄，且許多橋梁亦存在老舊裂化之問題，故需建立一套橋梁監、檢測系統針對橋梁安全性進行即時監測，且自動提供預警而封橋，確保橋梁通行之安全性，保障用路人之人身財產安全。本研究針對現地所使用之沖刷監測系統進行試驗與驗證，利用感測機制相似於現地監測系統之感測計安裝於縮尺模型進行沖刷試驗，以驗證沖刷系統之量測機制及確立其可靠性，此外亦透過縮尺模型之沖刷監測試驗，探討現行橋梁監測所量測得到的資訊所計算出支安全標準警戒值及行動值之合理性。 本研究之主軸即針對縮尺橋梁模型進行沖刷試驗，利用壓力感測計、沖刷振動感測計、浮球系統做為沖刷深度量測、觀測之主要沖刷監測系統，而以內視攝影機、手持式水下攝影機及鉛錘作為輔助性之沖刷深度量測，並藉由初步試驗估算土壤參數條件，進行破壞模式之計算，破壞模式區分為土壤承載力破壞、水流作用力傾倒破壞及基礎掏空之不穩定傾倒破壞進行分析，以計算縮尺橋墩於沖刷試驗中達到破壞傾倒時之安全係數是否達臨界標準，介以驗證參數分析及破壞模式之考慮，以提供跨河橋梁安全評估及封橋預警之標準建立。 本研究已藉由實驗室重現現地系統沖刷監測之可行性，所使用之安全係數分析理論已可在縮尺沉箱模型之沖刷倒塌破壞試驗中，預測其傾倒破壞時之沖刷深度範圍，且應用於縮尺橋墩模型之沖刷監測計可提供足夠之倒塌預警。

Taiwan is the island which is well known for its distinctive topography features. The central mountain range bisects the land from north to south resulting in most rivers have short courses and rapid streams. As a result, the scour effect could be seem as a critical problem for the bridge structure as the scale of natural disasters increase. The growing amount of bridge failure events in Taiwan due to typhoons and floods in recent years causing the public pay more and more attention towards the bridge safety under natural disaster, and the government and related organization also put a lot of efforts on such problem. This dissertation applies five kinds of sensing units which is based on the same sensing mechanism of developed scour monitoring system to laboratory experiments. Sensing units includes micro-electro-mechanical systems based pressure sensors, vibration-based detection sensors, floating ball, inner camera and handheld camera. The main purpose of this research is to verify the feasibility of developed monitoring system and to establish a warning benchmark by conducting the various test using reduced scale bridge structure model in laboratory. The feasibility of the developed monitoring system has been verified in laboratory by several experiments. The scour depth measurement by using accelerometers and the floating ball have been successfully applied to experiments, and it could be observed and confirmed that the scour depth can be regarded as the major parameter for the safety evaluation of caisson foundation bridge. Modes of scour failure for bridge structure are complex with many uncertainties, but the proposed sensing mechanisms for scour early warning could be achieved.