非飽和土壤光纖感測三軸試驗裝置之研發與應用

Abstract

目前室內土壤試驗中所使用的量測儀器均以電子式感測器為主，在非飽和土壤三軸試驗中，為決定基值吸力對剪力強度的影響，使吸力達到平衡需耗費之試驗時間較長，而電子式感測器易受電磁波干擾，在長時間處於浸水或潮濕環境也容易發生短路故障以及訊號飄移等缺點。 本研究目的為利用光纖光柵多工、高靈敏度、高穩定度及不會短路等優點，應用布拉格光纖光柵(Fiber Bragg Grating, FBG)做成的感測器來全面取代傳統三軸試驗裝置中所使用之電子式荷重元、位移計與壓力計等。本論文首先介紹光纖光柵感測器設計原理與感測器之室內標定，最後進行非飽和土壤三軸試驗以評估非飽和土壤光纖感測三軸試驗裝置之可行性與準確性。

The response of soil sepcimen in a triaxial cell is typically monitored using electronic sensors. For triaxial tests on unsaturated soil specimens, a long period is generally required to allow matrix suction within the specimen to reach a stable value. The eletronic sensors are subject to electro-megnatic interference (EMI) and prone to zero shift and short circuit when exposed in water for a prolonged period. The objective of this research is to develop and verify the feasibility for a trixial testing device to be intrumented cimpletely using Optic Fiber Bragg Grating (FBG) sensors. The FBG instrument includes a load cell, gauge and differential pressure transducers and a linear displacement sensor. This set up takes advantage on the distributive, high sensitivity/stability and immune to EMI and short circuit characteristics of the FBG sensors. The thesis introduces the basic principles of FBG sensors and their calibrations. Procedures of using this sensors in a series of unsaturated soil tests and their results are described. The feasibility and accuracy of the FBG sensors are evaluated.