TDR與OTDR錯動變形監測之研究

Abstract

一直以來，錯動變形監測在大地工程扮演著相當重要的地位。隨著通信及電子技術之演進，傳統之錯動變形量測設備已跟不上時代之脈動。時域反射法(TDR, Time Domain Reflectometry) 具有遠端即時監測之特性，其先進的被動式監測技術應用在錯動變形監測上，更是錯動變形監測的一項創新。TDR在錯動變形監測上，能定出地層發生錯動之位置，隨著錯動量之增加，亦可明顯由反射訊號得知其增量之趨勢。但美中不足的是，在錯動變形量化上，受到纜線電阻及現地破壞模式之影響，至今仍無量化錯動量之通用方式。 本研究主要考慮薄剪破壞模式，以考慮纜線電阻之傳輸線波傳理論模擬不同電纜長度受剪之TDR反射訊號，並以阻抗及錯動量之唯一性關係量化錯動量。光時域反射儀(OTDR, Optical Time Domain Reflectometer)光纖傳輸具有低衰減與可偵測缺陷點位置與損失之特性，故引進OTDR結合TDR錯動變形試驗，找出錯動事件點之位置，並試圖探討錯動量與光損失之關係。 由本研究結果顯示：在不考慮剪力帶寬度下，以同一個感測電纜下，連接不同延長線長度(2m、10m、20m及30m)均可模擬出近似之TDR反射波形，並得出阻抗-變位之唯一性關係；OTDR光纖對錯動變形量測初始反應較TDR感測電纜佳，其低衰減之特性，可做遠超過TDR感測電纜長度之長距離量測，唯其在錯動變形量之量測範圍較TDR感測電纜小。TDR感測電纜與OTDR光纖在錯動變形之量測上，可形成互補的效果。

Monitoring of slip displacement has been employed in the Geotechnical engineering for many years. With the evolution of the communication and electronic technology, the traditional slip-displacement monitoring device has fallen behind. The application of TDR passive monitoring technique on the slip displacement monitoring is an innovation. TDR can be used to determine the position of slip displacement and find the trend of increment of the displacement from the reflective signal in slip displacement monitoring. Unfortunately, the quantification of slip displacement is affected by the cable resistance and complex failure modes in field strata, and there has not been generalized method for quantifying the slip displacement magnitude. This study focuses on the thin shearing mode. Transmission line theory considering cable resistance is utilized to simulate the TDR waveforms of a sensor cable subjected to shearing with different lead cable length. The relation between the impedance and slip displacement magnitude is used to quantify the displacement magnitude. Taking advantages of the low attenuation characteristics of optical time domain reflectometry (OTDR), this study also explores the OTDR system for slip displacement monitoring and discusses the relation between displacement magnitude and light loss. The result shows that the TDR waveforms of different slip displacement and lead cable length are successfully simulated by the developed algorithm and the relation between the cable impedance and slip displacement magnitude can be uniquely obtained. The sensitivity of the OTDR system is superior to that of TDR system. The OTDR system can detect much longer sensor distance than TDR due to its low attenuation but the measuring range of slip displacement for the OTDR system is smaller than that for the TDR system. On the slip displacement monitoring, the TDR and the OTDR system can be complementary.