光纖光柵地層移動監測技術之研發

Abstract

如何藉地層內的變形分佈監測，做為邊坡或檔土結構破壞前 (Pre-failure)預警或提供結構物行為分析參數，是一個非常不容易的事情。要量得地層內的局部變形，需要非常穩定與高靈敏度的儀器，現今常用量測之工具包括測傾儀(Inclinometer)與伸張儀(Extensometer)，這類電子感測器在現地長期使用時，具有易受潮與雷擊損壞、易受電磁波干擾與非分佈式感測等缺點。本研究選擇光纖光柵(Fiber Bragg Grating, FBG)作為新的感測元件，研發符合感測局部地層變形所需之光纖感測器。光纖光柵具有體積小、不受電磁波干擾、可長距離傳輸訊號與一條線上可多點感測之優點。本研究所研發出之光纖地層位移感測器包括FBG應變管(FBG Pipe Strain Gauge, FBG-PSG)與FBG節理式偏斜儀(FBG Segmented Deflectometer, FBG-SD)兩種。FBG-PSG現地灌漿埋設後穩定度較高且現地裝設較容易，但FBG-PSG結果解釋有其理論上之缺陷，且FBG-PSG無法更新維護與重覆使用。FBG-SD單一組的偏斜量測解析度可達0.001度，實驗室內的環境測試實驗、9米測傾管室內標定實驗與台北市深開挖擋土壁側向變形量測實驗，證明了FBG-SD的可靠性與功能性。FBG-SD於黃河河堤丁壩的安全監測實驗，則證明FBG-SD在海(河)堤邊坡非犧牲式安全監測的可行性，同時也驗證FBG-SD感測系統可提供長期有效且經濟的安全監測。

The technique to measure ground displacement profile for the purpose of providing pre-failure warning or parameters for earth retaining structural design is rather challenging. Highly sensitive and stable sensors would be required to measure the ground displacement profile. The commonly used sensors such as the inclinometer or extensometer are electrical devices. These devices are non-distributive in nature, and prone to damage by moisture and/or lightning when deployed in the field for prolong period. Sensing devices that are based on optic Fiber Bragg Grating (FBG) have been developed to monitor ground displacement. The unique advantages of FBG include its small dimensions, immune to electromagnetic interference (EMI), capable of sharing the same optic fiber by multiple sensors and long distance signal transmission. The ground displacement monitoring devices developed in this research include the FBG Pipe Strain Gauge (FBG-PSG) and FBG Segmented Deflectometer (FBG-SD). The FBG-PSG can be grouted in place. The system is stable and easy to install. However, there are drawbacks in numerical interpretation of the FBG-PSG readings and the FBG-PSG is not re-usable. The FBG-SD is capable to detecting deflections with a resolution of 0.001 degree. The device has been tested in a thermal chamber to verify its durability. Laboratory calibration of the FBG-SD has been conducted using a set of 9m long inclinometer casings. Field application has been carried out to monitor the deflection of a diaphragm wall at a deep excavation project in Taipei. The reliability and functionality have been verified using this series of experiments. A field test using FBG-SD for safety monitoring at a spur dike on Yellow River in China has been carried out. The test shows that it is feasible to use FBG-SD as a non-sacrificial, long term, reliable and economic means to monitor the safety of river/ocean dikes.