適用於橋樑沖刷監測之TDR感測器研發

Abstract

近年來，因氣候變遷關係，台灣地區洪水災害發生頻率上升，加上台灣地形陡峭，河川又多屬狹窄急短的型態，使得河川沖刷機制非常旺盛。嚴重的沖刷常導致橋樑基座淘刷以致橋樑倒塌，不僅日後維護整治經費高，更危及了民眾生命安危。而沖刷監測除可輔助橋梁安全監測使用外，更能提供相關沖刷模式率定使用，然而現階段運用在監測橋樑沖刷雖有許多各式各樣的儀器，除了需具備有即時監測功能外，仍有洪水沖刷下之耐久性實務問題需要著手克服。 本研究將利用時域反射法（Time Domain Reflectometry, TDR）傳輸線式之優勢，研發適用於土壤與岩石河床之感測器，進而量測沖刷資訊。第一階段實驗以模擬鑽桿型式之感測器研發為主，係利用金屬鑽桿配合槽溝施作，以埋設另一導體形成導電路徑。其實驗結果定性發現隨槽溝開放的角度及內外導體的間距加大，量測結果的靈敏度也跟著提升。第二階段進行鋼索式之感測器研發為主，其實驗結果發現，導體的材質影響能量的傳遞、導體的大小配置決定感應的範圍、回填料的粒徑大小決定感測器周圍回填材之土壤固體之體積含量比例，皆是影響量測結果靈敏度之因素。綜合多項實驗結果及現地安裝之考量，本研究將採用鋼索式的感測器以進行現地試驗的探討。 為配合定量分析沖刷行為，本研究基於相關文獻初步提出全走時分析法，然而受限於絕緣感測器量測效能與參數率定方式，本研究另外提出土水段走時分析方法，並建議配合絕緣感測器於不同材質下電磁波走速率定模式，建置絕緣感測器現地率定方法與標準沖刷分析程序。因此本研究基於上述研究成果，初步於東勢大橋進行現地試驗，並設置即時監測系統，以能有效期望紀錄洪水所造成之刷深與回淤深度，初步成效良好，但仍須進一步修正現場波形穩定性，期以提供自動化資訊予橋樑管理者。

Rivers in Taiwan have features of narrow shape, deep slope, and high flow velocity, aggravating bridge scour. Severe scouring would decrease the pier bearing capacity such that the bridge may collapse, and this failure will not only increase remediation cost, but also endanger the safety of people's lives. To minimize the aformentioned influences, the bridge scour monitoring provides a way of bridge safety assurance, it also supports the in-situ verifications of scouring mechanism model calibration. Many kinds of instruments or techniques are proposed for the bridge scouring monitoring; however, a real-time monitoring method with high durability still needs to be developed. This study used Time Domain Reflectometry (TDR) technique to develope sensor applicable to both soil and rock scour. The first phase of the sensor development was aimed to work with drill rods. The TDR drill rod sensor is composed of metal drill pipe with a ditch that buried another conductor for the formation of sensing waveguide. Experimental results indicated that with more open angle of ditch and larger spcing between two conductors, the sensitivity of the measurement increases The second phase of the sensor development was the wire type. Results revealed that the conductor material affects energy transfer, and the conductor size of the configuration decides sensing range. Furthermore, the particle size of the backfill material in borehole also determines measurement sensitivity. Quantitative analysis of TDR scouring was also proposed in this study. The scouring estimation with acceptable accuracy was accomplised by interpreting the travel time of the soil-water section, and with calibrated electromagnetic wave velocities of the sensor in materials. Finally, this study used a TDR wire type sensors and corresponding analysis method for in-situ testing in the Tung- Shih Bridge. The recorded scouring data of bridage piers is preliminarily verified. However, modified construction procedure is suggested to stabilze the measuredwaveformsfor data reduction.