TDR地滑監測系統與測傾管共構可行性探討

Abstract

目前於山坡地進行滑動監測大部分使用傳統測傾管採用一組測傾儀定期以人工方式進行孔內移動測讀，除了量測過程耗人力耗時間、空間解析度較差、監測頻率不佳、也有於邊坡監測的壽命較短之問題；TDR錯動變形運用於大地工程已行之多年，其優勢為可遠端自動化並可與其他量測物理量的TDR感測器結合，一機多功用減少監測成本。本研究之主要目的在於探索與發展更經濟務實、適用於大規模深層滑動邊坡的監測系統，期望能結合測傾管與TDR 的優點，發展能與測傾管共構的TDR地滑監測系統，以大幅降低監測系統的設置成本。 本研究利用數值模擬探討TDR監測纜與測傾管共構後的互制行為後，於實驗室建立一套與現地邊界條件相符之模型:錯動變形物理模型，據以了解纜線-測傾管-灌漿材複合材料受剪後TDR反射訊號對應外部剪力盒位移量之關係，探討TDR監測纜與測傾管共構之可能性，最後於苗栗縣鹿場台地上進行現地測試，利用研究結果與現地安裝經驗提出TDR錯動變形與測傾管共構監測之安裝程序及量化分析，提供實務應用的參考。 本研究充分探討纜線擺放位置、纜線與測傾管之間間距、管徑影響，數值模擬與物理實驗皆顯示，將纜線放在測傾管之B向且將兩者距離拉遠對於纜線的反應較靈敏，而小管徑的測傾管與纜線靈敏度較大，另外，利用節點於剪動量10cm內有提升纜線的靈敏度，但對於提早偵測變形沒有幫助，於後能繼續探討。現地測試之資料顯示邊坡於初期產生訊號時共構纜線仍有反射訊號，且能延長監測孔之壽命，後續仍需持續監測。

Inclinometers are conventionally used to monitor subsurface movements, but there are some disadvantages in this technique. In recent years, Time Domain Reflectometry (TDR) is a relatively new technique based on transmitting an electromagnetic pulse to automatically and continuously measure localized deformations in rock and soil. The aim of this study is to combine Inclinometer and TDR’s advantages to develop a better slope monitoring system. This study investigated the feasibility of integrated monitoring system, consisting of coaxial cable and inclinometer casing in detecting subsurface slope deformation. Numerical simulation was performed and a physical model was constructed that mimic the field condition in order to evaluate the performance of the proposed integrated slope monitoring technique. At last, installing standalone TDR and integrated TDR (with inclinometer casing) monitoring system on Luchang platform as field experiment. According to this study, the suggested procedure of integrated TDR and inclinometer installation and interpretation was revised for better practical use. The interaction factors (including the location of cable, the gap between cable and casing, the casing size) between the TDR cable and inclinometer was investigated. The results of numerical simulation and physical test showed a similar pattern: cable setup at side ‘B’ and as far as possible from the inclinometer casing provided better sensitivity of TDR response. The sensitivity of TDR response was found relatively dependent on the size of inclinometer casing. The amplifier attached on the cable were found useful to improve the sensitivity to shear displacement (4~10cm)but didn’t effect on enhancing the early detectability. On the other hand, field monitoring data at Luchang demonstrated that reflection signal was generated at the slope sliding surface for both the standalone TDR cable the integrated TDR cable at side B of ABS casing, implying stiff sharp shear plane. The inclinometer probe could not be lowered below 56.5m after July 2017, but TDR cables were still workable at full length. TDR monitoring system extended the workable lifespan of the borehole. TDR signal of both installed system in Luchang platform were monitored continuously for further reflection signal comparison.