光纖光柵圓錐貫入儀之研發

Abstract

圓錐貫入儀是使用現地試驗方法取得土壤參數常用之方法。現今圓錐貫入儀大多以電子式的為主，而電子感測器常因所供應之電壓、周圍電磁波干擾等問題，比較容易有雜訊干擾的現象產生；電子迴路也常因為受潮而造成短路。本研究企圖利用光纖光柵(optical fiber Bragg Grating, FBG)不受水及電磁波干擾、一線多點量測的優點，研發FBG感測之震測與水壓量測功能之圓錐貫入儀（seismic-piezo cone penetrometer, SCPTU）。錐尖阻抗（qc）及摩擦套筒（fs）量測位置上加入各四組FBG做為應變感測器，以消除偏心受力所造成之影響。錐尖後方安裝FBG水壓計以及雙向之FBG加速度計。作者於室內進行新研發之SCPTU標定，配合電子式圓錐貫入儀於台北市關渡平原施作現地試驗，並進行比對。本論文敘述FBG SCPTU之設計原理，現有之試驗室與現場試驗結果，評估新研發SCPTU之功能並對未來改進提出建議。

Cone penetrometer is a popular in situ testing method often used to obtain soil parameters. Most of the currently available cone penetrometers are electrical; the test signals can be noisy due to fluctuations of power supply and electromagnetic interferences (EMI). The electrical circuit is subject to short circuit when exposed to moisture. This research intends to take advantage of the unique capabilities of optical fiber Bragg Grating (FBG) that include being immune to short circuit, EMI and able to connect multiple sensors on a single fiber, and develop an FBG sensored seismic-piezo cone penetrometer (SCPTU). The cone tip resistance (qc) and sleeve friction (fs) are respectively measured with four sets of FBG’s that served as strain sensors, and to offset effects of miss-alignment of forces imposed on the cone tip. Behind the cone tip sit an FBG pore pressure sensor and a pair of FBG seismometers. The author conducted laboratory calibration of the newly developed SCPTU, and performed field FBG and electrical SCPTU concurrently at a test site in Guan-Du Plain, Taipei. The thesis describes the design principles of the FBG SCPTU, available laboratory and field test results, evaluates the capabilities of the new SCPTU and provides recommendations for future improvements.