應用於地工離心機之光纖光柵微型孔隙壓力計研發

Abstract

電子式微型孔隙壓力計被廣泛應用在地工離心機模型試驗中，量測試體內部之孔隙壓力變化，其中以奇異電子(GE Sensing and Inspection Technolo-gies)所生產之Druck PDCR81系列最受歡迎。經驗指出此類電子式感測器容易受到離心機運轉所產生之電磁波影響。由於其應變膜片係採用矽晶材料組成，感測器之率定曲線可能會在離心機試驗後改變，且在負壓範圍內無法得到良好的線性度與重複性。諸多問題使得在離心機模型實驗中可能無法獲得可靠的量測成果。為了克服以上問題，本研究使用光纖光柵作為量測單元，利用其不受電磁波與水影響之優點，製作微型化孔隙壓力計以取代傳統電子式感測器，並在英國劍橋大學之地工離心機進行測試，驗證其功能。論文敘述本研究之背景、光纖光柵微型化孔隙壓力計之設計原理以及功能之驗證成果。

Electrical miniature pore pressure transducers (PPTs) have been widely used in geotechnical centrifuge modelling tests to measure the pore pressure variations in the test specimen. Among the available sensors, Druck PDCR81 series produced by GE Sensing and Inspection Technologies has been the most popular one. However, this electrical sensor can be affected by electromagnetic interference (EMI). Since the sensor diaphragm is made of silicon, the calibration factors can vary after a centrifuge test. In addition, the Druck PDCR81 PPTs may not work repeatedly with a linear response under negative pressure. These problems may lead to unreliable test results. To overcome these drawbacks, a miniature PPT was developed using optical fiber Bragg grating (FBG) as the sensing element in this research project. The design takes advantage of the unique capabilities of FBG that it is immune to EMI and moisture. A geotechnical centrifuge modelling test was performed at the University of Cambridge for verification of the FBG based PPT. The thesis describes the background of the research, design principles of the new FBG PPT and its performance based on available test results.