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A comprehensive framework of TDR landslide monitoring and early warning substantiated by field examples
(2019-11-28)
Chung, Chih-Chung
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Lin, Chih-Ping
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土木工程學系
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Department of Civil Engineering
Due to the climate change and hazardous geological environment in Taiwan, real-time landslide monitoring for safety of adjacent tribes or infrastructures is much conspicuous. Time domain reflectometry (TDR) is considered as valuable technology for continuously capturing dynamics and locations of shear deformations with high temporal and spatial coverages. In this study, a comprehensive framework was proposed by integrating up-to-date procedure of installation guide, data acquisition, sliding deformation identification, and early warning processing. The advantages of the proposed framework were then examined and substantiated via field cases. The first case is at a large colluvium slope in Lushan, central Taiwan. The colluvium is still active after heavy rainfall events, but limited evidence of sliding characteristic was collected previously by manual inclinometer logging. Therefore, the TDR framework was deployed and multiple landslide surfaces at great depths were timely observed. Movement of colluvium mass was thereby interpreted as a buckling fold. Additionally, creep occurred among the colluvium layer during the monsoon season because of strength weakening influenced by pore pressure fluctuations. Monitoring results of the second landslide case in Jufan, northern Taiwan, reported the dynamics of a thin sliding plane captured with TDR high temporal resolution. This unique behavior was further applied for devising of a novel early-warning strategy in terms of time-variation of TDR response, validating that the comprehensive framework of TDR landslide can effectively contribute to early warning.
Investigation of non-unique relationship between soil electrical conductivity and water content due to drying-wetting rate using TDR
(2019-03-26)
Chung, Chih-Chung
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Lin, Chih-Ping
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Yang, Shi-Hui
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Lin, Jhe-Yi
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Lin, Chun-Hung
The characterization of the relationship between volumetric soil water content (theta) and bulk electrical conductivity (EC) (or electrical resistivity) is of high interest in fields of engineering, fundamental petrophysical, hydrological model parameterization, and quantitative hydrogeophysical interpretations. Based on the relationship, for instance, the broad-area image using electrical resistivity tomography (ERT) can be transformed into theta tomograms as initial/boundary conditions of the slope stability analysis. However, the relationship is affected by the hysteresis, leading the inconsistency in drying-wetting circles. Therefore, this study focused on the factor of soil drying-wetting rate using the proposed time domain reflectometry (TDR) method and related sensors for such characterization. A modified pressure plate apparatus enhanced by TDR was first employed with a relatively low rate in which EC and theta were measured simultaneously, without evident non-unique relationship. A TDR penetrometer was then designed for acquiring the temporal variations of theta and EC in the field. On the basis of certain assumptions, observations showed an apparent dependency of the slope of the theta-EC rating curve on rates, but no hysteresis pattern. Finally, a laboratory controlled fast wetting drying cell was used to increase the response time, proving that both the hysteresis and slopes of the theta-EC rating curves were obviously affected by the soil drying-wetting rate, as a significant finding to the related topics.
A bundled time domain reflectometry-based sensing cable for monitoring of bridge scour
(2019-05-01)
Wang, Kai
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Lin, Chih-Ping
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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.
Application of geophysical methods in a dam project: Life cycle perspective and Taiwan experience
(2018-11-01)
Lin, Chun-Hun
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Lin, Chih-Ping
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Hung, Yin-Chun
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Chung, Chih-Chung
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Wu, Po-Lin
There is a growing demand for using non-destructive geophysical techniques to internally image dam condition and facilitate the early detection of anomalous phenomena. Near surface geophysical techniques have advanced significantly in the last few decades, and can play a significant role in the siting, construction, and operational safety and sustainable management of dams. Application of engineering geophysics in site characterization during feasibility investigation phase is already part of the standard of practice. This paper introduces newer applications of engineering geophysics during construction phase, dam safety assessment, and sustainable management, including quality control of compacted soils, investigation of abnormal leakage in an earth darn, evaluation of an aged concrete dam, geophysical health monitoring for a newly-constructed dam, and monitoring of sediment transport for sediment management. The applications were presented with more emphases on the needs of dam engineering and adapting appropriate geophysical methods to make assessment more effective and consequential. The collage of these case studies is to broaden the view of how geophysical methods can be applied to a dam project throughout a dam's life cycle and strengthen the linkage between geophysical surveillance and engineering significance at all stages. (C) 2018 Elsevier B.V. All rights reserved.
New types of time domain reflectometry sensing waveguides for bridge scour monitoring
(2017-07-01)
Lin, Chih-Ping
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Wang, Kai
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Chung, Chih-Chung
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Weng, Yu-Wen
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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.
Development and implementation of horizontal-plane settlement indication system for freeway health monitoring during underpass construction
(2017-11-01)
Chung, Chih-Chung
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Lin, Chih-Ping
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Chin, Chi-Hsien
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Chou, Kun-Hsien
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土木工程學系
This study introduced two major contributions for freeway health monitoring during the pipe roof construction and subsequent excavation to enlarge an existing underpass. First, a horizontal-plane settlement indication system (HSIS) was developed to monitor inevitable settlement due to shallow overburden above the steel pipes. Second, the experience gained from the field monitoring program was detailed with emphasis on encountered problems and countermeasures for freeway safety decision-making. On the basis of two microelectromechanical systems tilt sensors embedded as a differential pair, HSIS effectively minimizes the effect of ambient temperature whose fluctuation was expected at shallow depth. The measurement accuracy (4mm) and repeatability (0.05mm) were verified experimentally. Thereby, three HSIS arrays were positioned in the freeway pavement to continuously detect local settlement and based on which to issue possible alarm. The RS485 data acquisition protocol, which is characterized by fast synchronized communication, was applied for HSIS to reduce the dynamic error due to heavy traffics. The observed settlement was close to the alarm threshold, which is considered as the combination effects of the simulated settlement and the penetrating deviation during the pipe roof construction. Furthermore, an approach to account for false vertical drift due to instability of the fixed point of HSIS was proposed such that the settlement behavior during excavation phase could be effectively described. The unique implementation is a benefit to further HSIS application in practice.
Improved TDR Method for Quality Control of Soil-Nailing Works
(2016-01-01)
Chung, Chih-Chung
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Lin, Chih-Ping
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Wang, Kai
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Lin, Chih-Sheng
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Ngui, Yin Jeh
Time domain reflectometry (TDR) has become an effective nondestructive testing method for soil-nailing inspection. Previous studies utilized a preinstalled, single-core, electric wire alongside the rebar within the soil nail. Measurements may be affected by possible grout defects and excessively overestimate the rebar length if the wire is coiled around the rebar. An improved TDR waveguide and a corresponding decoupled data reduction method (for both soil-nail length determination and grout condition inspection) are proposed herein. The feasibility and advantages of the new approach were experimentally verified with two types of TDR device. The proposed methodology makes it possible to use a portable, low-cost, and low-speed TDR device as a quick and economical tool for quality control of soil nailing.
An Improved Modeling of TDR Signal Propagation for Measuring Complex Dielectric Permittivity
(2015-12-01)
Lin, Chih-Ping
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Tang, Shr-Hong
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Lin, Chun-Hung
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Chung, Chih-Chung
;
土木工程學系
Time domain reflectometry (TDR) is a measurement technique based upon transmission line theory. The solutions of transmission line equations are reformulated in terms of independent physical properties, instead of coupled per-unit-length circuit parameters. The complete TDR response is effectively modeled by a non-uniform transmission line using the non-recursive ABCD matrix approach. Approaches to calibrate line parameters and perform TDR measurements based upon such model are introduced with an example on dielectric spectroscopy. TDR modeling in terms of decoupled physical parameters and non-recursive algorithm allows more convenient calibration of line parameters and facilitates interpretation of TDR measurements.
Characterization of Electrical Properties by Time Domain Reflectometry
(2014-01-01)
Lin, Chih-Ping
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Lin, Chun-Hun
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Chung, Chih-Chung
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Liu, Hsin-Chan
;
土木工程學系
The monitoring and mapping of contaminated soil frequently involve geophysical prospecting methods as a complement to conventional geological, chemical and hydrological studies. Non-destructive geophysical techniques help to rapidly detect contaminants in soils and to monitor the extension of polluted areas. To go beyond structure characterization to composition and process interpretation, it is necessary to understand the relationship between the electrical properties of contaminated soils and soil compositions including the pollutants. The objective of this study is to develop a broadband measurement technique for more complete electrical characterization of contaminated soil including complex dielectric permittivity and electrical conductivity. The development is based on the time domain reflectometry, which is suitable for both laboratory and field measurements. The measurement system is easy to set up, calibrate, and operate to facilitate more investigations of electrical properties of various contaminated soil in relation to soil composition and contaminant content. It is also this study\'s intention to develop a technique that can be easily adapted to penetration probe for field investigation and monitoring.
Monitoring of Sediment Transport in a Reservoir using Time Domain Reflectometry
(2013-01-01)
Chung, Chih-Chung
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Lin, Chih-Ping
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Wu, Po-Lin
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Hsieh, Sheau-Ling
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Wu, Ching-Hsien
Due to geological weathering and climate change, soil erosion in watershed is becoming a serious problem in Taiwan. Large amount of sediment transports to reservoirs during typhoon events and affects the water quality. Density currents in reservoirs have high sediment concentration. The accumulated sediments have significantly reduced the reservoir capacity. Monitoring of sediment transport in a reservoir plays an important role in reservoir management. The existing techniques for suspended sediment concentration (SSC) monitoring, such as optical and acoustic methods, are sensitive to particle size or limited in measurement range. Furthermore, these techniques may not be cost effective for field monitoring due to the required maintenance and spatial coverage. A new technique based on time domain reflectometry (TDR) was recently introduced. It possesses several advantages including particle-size independence, low-cost transducers, durability, and cost-effective multiplexing. This study modified the TDR technique for better field applicability and demonstrated how it can be deployed as a full monitoring program for reservoir management through a case study in the Shihmen reservoir, Taiwan. Monitoring stations at upstream riverbank and outflow channels were installed with fixed protective structures to provide inflow and outflow sediment-discharge records. To capture the characteristics of density currents, multi-depth monitoring stations were designed and deployed on floats in the reservoir. Some of the data collected during Typhoon Fung-Wong are presented as an example to demonstrate the effectiveness and benefits of the monitoring station.

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