纜線電阻對於TDR量測影響之理論模擬與應用

Abstract

時域反射法（time domain reflectomery, TDR）屬於傳輸線式感測技術，具有上孔式、多功能及多工化特色，感測方式兼具機械式感測技術可靠耐久的優點及電子式可遠端自動化監測的能力，故逐漸被廣泛應用於大地工程監測，與諸如土壤科學、環境科學、農業工程等材料性質量測相關領域。上述大部份研究與應用目前多半忽略或不考慮傳輸線電阻影響，但現地監測實際上經常需要相當長度延長線，因此傳輸纜線中電阻影響不可忽略，需要進行相關修正，方能準確量測。本研究提出可正確描述傳輸纜線電阻影響的通用性波傳模型，藉此通用模型探討纜線電阻對於材料性質量測相關影響，並藉由本模型與室內試驗，進一步討論纜線電阻、材料互制、剪力帶寬度對於錯動變形監測之影響與改善建議。研究結果顯示本模型可靠精確，能有效考慮纜線電阻影響，不同應用領域範例皆證明本模型為一相對簡易、有效率、且具高解析度的工具，適合於探頭設計、參數研究、資料闡釋、與反算分析，能顯著改善監測應用與材料量測應用分析合理性與結果。

Time domain reflectometry (TDR), which is based on the transmission line sensing technology, consists of an up-hole device that interrogates various mechanical transducers, providing the reliability, durability and capability of remote monitoring. As a result, it is increasingly used in geotechnical instrumentation and measurements of material properties related to soil science, environmental science, agriculture engineering, etc. Existing researches and current practice do not take into account the effect of cable resistance in the transmission line, which frequently becomes important when long lead cables are used in the field. This study developed a comprehensive TDR wave propagation model which can correctly describe and deal with the effect of cable resistance on TDR measurements. The effect of cable resistance on measurements of dielectric properties was investigated based on the comprehensive TDR model. In the application of shear displacement monitoring, effects of cable resistance, cable-grout-soil interaction, and shear band were properly discussed via model simulations and laboratory shear tests. Results show that the comprehensive TDR model is reliable, accurate, efficient, and capable of taking account of the effect of cable resistance. Examples of using the TDR model on various geotechnical applications demonstrate the model as a relatively simple, efficient, and high resolution tool for probe design, parametric studies, and data interpretation. Better data interpretations of TDR measurements are achieved with the assistance of the comprehensive TDR model introduced in this study.