| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 102 === 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.
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