磁環式FBG地層下陷感測系統之研發

Abstract

現有常用來監測地層下陷方法使用多個磁環安裝在同一鑽孔不同深度來監測地層沉陷隨深度之變化，磁環深度使用有刻度之銦鋼尺配合裝有磁感應開關，以目視來辨識，其主要觀測誤差來源包括深度判讀誤差，且判定磁環深度位置的方法不夠嚴謹，或當深度較深之量測時，探測感應器之訊號可能薄弱等缺點，本研究企圖利用既有之磁環式分層監測井，配合光纖之輕巧、不會受潮短路、可十公里以上之長距離傳輸等優勢，研發光纖光柵(FBG)感測器代來量測地陷測井內之磁環位置。作者於室內進行新研發之FBG probe試驗，包括乾式、浸水式及9m室內試驗，並於成功大學水工試驗所的監測井施作現地量測。本論文敘述FBG probe之設計原理，室內試驗及現地試驗結果，評估新研發FBG probe之功能及效益，並對未來改進提出建議。

Multiple megnatic rings installed at varous depths in a cased borehole have been used for ground subsidence profile monitoring. A graded metallic tape with a reed switsh at the bottom was dropped into the borehole. The depth was visually identified from the tape measurement when the reed switch was triggered by the megnatic ring. The method for depth reading is not rigorous and often result in errors. In a deep borehole, the reed switch signal can be weak. The objectives of this research are to develop a fiber Bragg (FBG) based probe to work with the existing multiple megnatic rings system for ground subsidence profile monitoring. The FBG probe takes advantage of the fact that optical fiber is light weight, immune to short circuit, and signal transmission can easily exceeds 10 km. The author performed a series of laboratory test using the new FBG probe under dry and submerged conditions, and in a 9 m inclinometer casing with multiple megnatic rings attached. Field experiment was carried out using an existing observation well at a National Cheng Kung University Hydraulic Tesing Laboratory test site. The thesis describes the principles of the FBG probe, results from the laboratory and field tests, evalauates the performance of the FBG probe and make recommendations for further improvements.