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Applicability and limitations of time domain reflectometry bridge scour monitoring system in general field conditions
(1970-01-01)
Wang, Kai
;
Lin, Chih-Ping
;
土木工程學系
;
Department of Civil Engineering
A real-time and durable system for scour process monitoring with sufficient spatial precision is in pressing need for bridge safety management. In light of this, an innovative bundled time domain reflectometry sensing cable was recently proposed to enhance the time domain reflectometry technique for scour monitoring. However, current development only dealt with the construction of bundled sensing cable and the corresponding new data reduction method. Before it can be put into practical use, issues related to the effect of hydrological conditions, long-distance measurement, and actual field implementation are yet to be investigated. This study used both numerical simulations and laboratory experiments to examine the time domain reflectometry signals in response to both scour and deposition in different water-level conditions. As a result, the first guideline of waveform classification and interpretation is newly proposed to validly determine scour depth under various field conditions. Since field measurements often come with significant signal attenuation from resistance loss of long cable and dielectric and conductive loss in the sensing section, numerical simulations and a series of full-scale experiments were also conducted to assess the time domain reflectometry scour measurement range. The maximum measurement range of the latest time domain reflectometry scour sensing cable was found to be about 6 m. Within this range, the maximum error of scour estimation is within 0.2 m. Considering the new findings, a field time domain reflectometry scour monitoring system using the bundled time domain reflectometry sensing cable was designed accordingly and implemented at a bridge for the first time. The monitoring system successfully captured the scour process during a storm event and revealed some practical issues for future improvement as well.
A bundled time domain reflectometry-based sensing cable for monitoring of bridge scour
(2019-05-01)
Wang, Kai
;
Lin, Chih-Ping
;
Chung, Chih-Chung
;
土木工程學系
;
Department of Civil Engineering
Scour monitoring is crucial for providing early warning of bridge safety and extending the knowledge of scour process. Traditional methods that rely on underwater instruments encounter difficulties in installation and operation in harsh fluvial environment. Time domain reflectometry (TDR)-based scour sensing wire was recently introduced as a promising technique to improve field deployment and durability. This study focused on further improving the concept of TDR sensing wire for better sensor package and performance. An innovative bundled bottom-up sensing cable was proposed to improve sensor durability and avoid the adverse effect of sensor fouling. The sensor durability is enhanced by twisting two sets of steel strands (as two opposing electrodes for the waveguide) around a coaxial cable into a composite sensing cable. The inner coaxial cable is introduced and armored by the sensing steel strands to direct TDR pulse to the bottom end before connecting to the sensing waveguide formed by steel strands for bottom-up sensing. Furthermore, taking advantage of a new data reduction method by using time-lapse differential waveform, robustness of system calibration and scour estimation is further enhanced. Experimental results revealed the optimal design of bundled TDR sensing cable, effectiveness of the bottom-up sensing approach, and better performance of the differential waveform method.
New types of time domain reflectometry sensing waveguides for bridge scour monitoring
(2017-07-01)
Lin, Chih-Ping
;
Wang, Kai
;
Chung, Chih-Chung
;
Weng, Yu-Wen
;
土木工程學系
Scour is a major threat to bridge safety, especially in harsh fluvial environments. Real-time monitoring of bridge scour is still very limited due to the lack of robust and economic scour monitoring device. Time domain reflectometry (TDR) is an emerging waveguide-based technique holding great promise to develop more durable scour monitoring devices. This study presents new types of TDR sensing waveguides in forms of either sensing rod or sensing wire, taking into account of the measurement range, durability, and ease of field installation. The sensing rod is composed of a hollow grooved steel rod paired up with a metal strip on the insulating groove, while the sensing wire consists of two steel strands with one of them coated with an insulating jacket. The measurement sensitivity is inevitably sacrificed when other properties such as the measurement range, field durability, and installation easiness are enhanced. Factors affecting the measurement sensitivity were identified and experimentally evaluated for better arranging the waveguide conductors. A data reduction method for scour-depth estimation without the need for identifying the sediment/water reflection and a two-step calibration procedure for rating propagation velocities were proposed to work with the new types of TDR sensing waveguides. Both the calibration procedure and the data reduction method were experimentally validated. The test results indicated that the new TDR sensing waveguide provides accurate scour depth measurements regardless of the sacrificed sensitivity. The insulating coating of the new TDR sensing waveguide was also demonstrated to be effective in extending the measurement range up to at least 15 m.
河川含砂濃度全洪程觀測與含砂濃度歷線推估模式建構(2/2)
(2015)
鐘志忠
;
Chih-Chung Chung
;
國立交通大學
台灣每逢颱風豪雨河川泥砂濃度即迅速飆升，而高濁度之水流往往對下游地區之水資源利用、河道穩定、河中構造物安全與生態系統等產生嚴重衝擊，因此瞭解颱洪期間河川泥砂濃度於時間與空間之變化實為重要課題。本計畫主要建立以物理概念為基礎之颱洪期間河川泥砂濃度歷線推估架構與方法，並配合時域反射法(Time Domain Reflectometry, TDR)河川泥砂濃度觀測資料以利於相關模式之建立、檢定與驗證。但由目前實務觀測經驗發現，現場感測器避免雜物干擾與落淤等限制需要克服，此外對於提供河川橫斷面泥砂濃度量測規劃與驗證仍須進一步探討。
河川含砂濃度全洪程觀測與含砂濃度歷線推估模式建構(1/2)
(2014)
鐘志忠
;
Chih-Chung Chung
;
國立交通大學
台灣因地形影響坡陡流急河川挾砂能力強，加以地質條件脆弱集水區產砂量高，每逢颱風豪雨河川泥砂濃度即迅速飆升，而高濁度之水流往往對下游地區之水資源利用、河道穩定、河中構造物安全與生態系統等產生嚴重衝擊，因此瞭解颱洪期間河川泥砂濃度於時間與空間之變化實為重要課題，以做為擬定流域土砂管理策略或評估高濁度水流對水土災害影響之參考。傳統上河川泥砂濃度多是利用以統計法所建立之流量與輸砂量經驗曲線進行推估，惟此法因未考慮流域泥砂生產與遞移之物理機制，無法解析集水區降雨於空間分布與雨型變化等對集水區泥砂遞移之影響，更無法適用於集水區環境發生變化後(如流域管理或河川治理)之河川泥砂濃度推估，因此實有必要建立以物理概念為基礎之颱洪期間河川泥砂濃度歷線推估架構與方法，以解決上述統計法所面臨之問題。無論是統計法之經驗曲線或利用物理概念建立之河川泥砂濃度歷線推估架構，皆須有準確之河川泥砂濃度觀測資料以利於相關模式之建立、檢定與驗證，而自動化且即時之泥砂觀測數據更可做為颱洪期間下游土砂災害預警與水資源設施即時操作之參考。目前河川水文站之泥砂觀測多仰賴人工取樣，常缺乏高流量下之泥砂濃度資料，因此水利署於2006~2009年度曾辦理以時域反射法(Time Domain Reflectometry, TDR)方式進行自動化泥砂觀測之先期研究，以同時獲得即時性、自動化與節省作業人力等特性，後續並於2011~2012年持續針對現地應用所發現之實務問題進行改善與提昇量測精度與穩定度，並建置對應之「泥砂濃度量測平台」，以提供觀測資料之查詢及展示，但由目前實務觀測經驗發現，現場感測器避免雜物干擾與落淤等限制需要克服，此外對於提供河川橫斷面泥砂濃度量測規劃與驗證仍須進一步探討。綜合以上所述，本計畫目的在以既有之固定式自動化泥砂觀測示範站為基礎，擬定持續維護既有固定式自動化泥砂觀測示範站穩定運作外，並針對實務應用所面臨之問題持續改善相關設備。此外，為進一步將泥砂觀測資料實務運用，將探討橫斷面泥砂濃度空間變異與量測機制評估。另一方面本計畫亦將探討流域泥砂生產與遞移之分析方法，提出以物理概念為基礎之颱洪期間河川泥砂濃度歷線推估架構，期使本計畫之即時監測系統與數據以及泥砂濃度歷線推估架構，做為後續集水區土砂管理策略擬定或流域綜合治理等相關計畫之參考。
TDR Method for Compaction Quality Control: Multi Evaluation and Sources of Error
(2012-09-01)
Lin, Chun-Hung
;
Lin, Chih-Ping
;
Drnevich, Vincent
;
交大名義發表
;
National Chiao Tung University
The use of the time domain reflectometry (TDR) method, designated ASTM D6780 (ASTM D6780, 2005, "Standard Test Method for Water Content and Density of Soil in Place by Time Domain Reflectometry (TDR)," Annual Book of ASTM Standards, Vol. 04.09 ASTM International, West Conshohocken, PA), to measure water content and soil density is relatively new with both successful and unsatisfactory results being reported. This paper reexamines the TDR method from various aspects, including laboratory investigation of the relation between TDR-measured electrical properties and soil phase parameters, full scale laboratory evaluation of the standardized methods, real world performance evaluation at construction sites of earth dams, and theoretical reexamination. Laboratory calibration reveals the effect of soil type on soil electrical properties, and its implication on the TDR method is discussed. The full scale laboratory evaluation supports the validity of both the one-step and two-step TDR methods. But the field evaluation at construction sites of earth dams indicates otherwise, particularly in the measurement of soil density. The errors in the two-step method are attributed to the penetration disturbance of the field multipole resonance probe (MRP). An additional source of error in the One-Step method is found to be a theoretical flaw in the current empirical adjustment process for correcting the variation of pore-fluid conductivity from the calibration test to field measurements. Remediation for the two-step method and updating of the ASTM D6780 to overcome the shortcomings of the one-step testing are in progress.
Development of TDR penetrometer through theoretical and laboratory investigations: 2. Measurement of soil electrical conductivity
(2006-07-01)
Lin, C. P.
;
Chung, C. C.
;
Tang, S. H.
;
交大名義發表
;
National Chiao Tung University
A TDR penetrometer was introduced to allow simultaneous measurements of dielectric permittivity and electrical conductivity during cone penetration. This study focused on the theoretical development and experimental evaluation of electrical conductivity measurement using the TDR penetrometer. Theoretical development takes into account the cable resistance and nonconducting cone shaft, leading to a new data reduction equation and calibration procedure. Measurement sensitivity and spatial sampling bias were experimentally evaluated for various probe configurations. The results show that the measurement sensitivity of interest may be controlled by the geometric factor of the probe. The complication and implications of the spatial weighting bias are discussed. A prototype TDR penetrometer was calibrated and used to perform simulated penetration tests in a soil. Experimental results do not show significant errors in electrical conductivity due to the penetration disturbance, verifying the effectiveness of the TDR penetrometer for electrical conductivity measurement.
Comprehensive wave propagation model to improve TDR interpretations for geotechnical applications
(2007-03-01)
Lin, Chin-Ping
;
Tang, Shr-Hong
;
交大名義發表
;
National Chiao Tung University
Time domain reflectometry (TDR) is becoming an important monitoring technique for various geotechnical problems. Better data interpretation and new developments rely on the ability to accurately model the TDR waveform, especially when long cables are used. This study developed an efficient, complete, and general-purpose TDR model that accounts for all wave phenomena including multiple reflection, dielectric dispersion, and cable resistance all together. Inverse analysis based on the TDR wave propagation model is proposed to calibrate the TDR system parameters and determine the TDR parameter that changes with the physical parameter to be monitored. Calibration of TDR cable and data interpretations for various geotechnical applications were demonstrated with laboratory experiments. The excellent match between the simulated and measured waveforms validates the TDR wave propagation model. The results show that the proposed numerical procedure is a relatively simple, efficient and high-resolution tool for probe design, parametric studies, data interpretation, and inverse analyses. This study should provide a sound theoretical foundation for further TDR developments in geotechnical monitoring.

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