Browsing by Author "Lin, Chih-Ping"

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3D and Boundary Effects on 2D Electrical Resistivity Tomography
(2019-08-01)
Hung, Yin-Chun
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Lin, Chih-Ping
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Lee, Chin-Tan
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Weng, Ko-Wei
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土木工程學系
Electrical resistivity tomography (ERT) is one of the most widely used geophysical methods in geological, hydrogeological, and geo-environmental investigations. Although 3D ERT is now available, 2D ERT remains state-of-the-practice due to its simplicity in fieldwork and lower space requirements. 2D ERT assumes that the ground condition is perpendicular to the survey line and outside the survey line is homogeneous. This assumption can often be violated in conditions such as geologic strikes not perpendicular to the survey line and topographic changes or buried objects near the survey line. Possible errors or artifacts in the 2D resistivity tomogram arising from violating the 2D assumption are often overlooked. This study aimed to numerically investigate the boundary effects on 2D ERT under various simplified conditions. Potential factors including resistivity contrast, depth and size of buried objects, and electrode spacing were considered for the parametric studies. The results revealed that offline geologic features may project onto the 2D tomogram to some extent, depending on the aforementioned factors. The mechanism and implications of boundary effects can be drawn from these parametric studies.
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
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土木工程學系
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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.
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.
A novel TDR signal processing technique for measuring apparent dielectric spectrum
(2017-01)
Lin, Chih-Ping
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Ngui, Yin Jeh
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Lin, Chun-Hung
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交大名義發表
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National Chiao Tung University
Conventional time-domain reflectometry (TDR) signal interpretation generated single-valued apparent dielectric constant, while sophisticated, inconvenient measurement system and analysis is needed for measuring spectral complex dielectric permittivity (CDP). Niching between these approaches, a novel phase velocity analysis (PVA) method is developed to efficiently measure apparent dielectric spectrum (ADS) directly from TDR signals in a simple, quick, model-free, and inversion-free manner. The proposed PVA method extracts the two reflections from the top and end of the sensing probe by proper window selection and calculates their phase shift at each frequency, from which the phase velocity and corresponding apparent dielectric constant can be determined. Numerical and experimental results demonstrated that PVA is capable of measuring ADS in a frequency band, typically from 100 MHz-1 GHz. The effect of signal truncation was identified as the main cause of poor results outside the effective frequency band. Factors that affect the frequency band of effective ADS were numerically investigated. For highly dispersive materials, the end reflection pulse does not fully develop before the arrival of subsequent multiple reflections, resulting in severe truncation error and decreasing the upper frequency of effective ADS. Methods to estimate and extend the frequency band of effective ADS were further proposed. The simple procedures behind PVA, and its computationally efficient nature, make this method suitable for field monitoring. The resultant ADS is a potential improvement to current applications utilizing a travel time approach.
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
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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.
Applicability and limitations of time domain reflectometry bridge scour monitoring system in general field conditions
(1970-01-01)
Wang, Kai
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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
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.
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.
Application of surface wave method in assessment of ground modification with improvement columns
(2017-07-01)
Lin, Chun-Hung
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Lin, Chih-Ping
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Dai, Yung-Zheng
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Chien, Chih-Jung
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交大名義發表
Surface wave testing is considered a promising method for assessing average property and actual area replacement ratio of ground modification with improvement columns, owing to its non-destructive nature and large sampling range. However, the surface wave method is essentially a 1-D method assuming horizontally-layered medium. What it measures in highly heterogeneous improved ground remains to be investigated. This study aimed at evaluating the feasibility of surface wave method in the heterogeneous ground with improved columns, and investigating the homogenization of shear wave velocity and the lateral sampling range. Field tests on a jet grouted construction site showed that the surface wave method worked well in such heterogeneous grounds and yielded a site-representative shear wave velocity profile regardless of the survey location. This is attributed to the survey condition where the wavelength is greater than the spacing of grout columns. 1-D analytical models and 2-D numerical simulations were conducted to investigate the quantitative relation between construction parameters and the percentage increase of shear wave velocity after ground improvement. A quantitative approach to estimate the area replacement ratio and overall quality of improvement columns by surface wave testing is proposed. (C) 2017 Elsevier B.V. All rights reserved.
Applications and challenges of near surface geophysics in geotechnical engineering
(2015-08-01)
Lin, Chih-Ping
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Lin, Chun-Hung
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Wu, Po-Lin
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Liu, Hsing-Chang
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Hung, Ying-Chun
Geophysical exploration methods have been applied to geotechnical engineering problem since their early developments. However, the results often do not live up to engineers\' expectations. Works still need be done before we see the widespread use of geophysical methods in engineering practice. This study provides an overview of newer developments and applications of near surface geophysical techniques in geotechnical problems. More importantly, the limitations and challenges of current geophysical methods in this context are identified and possible countermeasures are proposed. Near surface geophysical techniques, such as travel time velocity tomography, electrical resistivity tomography (ERT), and multi-channel analysis of surface wave (MASW), have advanced significantly in the last couple of decades within the scientific community. The applications of these methods in Taiwan\' s geotechnical problems are first examined, including assessment of liquefaction potential, evaluation of dam safety, investigation of soil and groundwater contamination, and quality control and assurance of ground improvements. The seismic travel time tomography was selected to examine the integrity of a concrete dam in terms of P-wave velocity. ERT was used to investigate abnormal seepage in earth dams and soil and groundwater contamination. Shear-wave velocity profiles non-destructively obtained by MASW are relevant to many traditional geotechnical problems, in which the quantitative assessment of liquefaction potential and ground improvements were particularly presented. The effectiveness of these applications is discussed from an engineer\'s perspective, and the associated challenges and practical countermeasures are systematically addressed. The velocity imaging of the concrete dam was quite successful and promising, allowing the engineer non-destructively "CT scan" the strength of the dam body. ERT works in a similar fashion for water-related problems. However, the results on abnormal dam seepage and groundwater contamination were less conclusive since the resistivity depends both on pore-water properties and geological factors. So it\'s important to integrate geological background and results from geotechnical investigation or monitoring. In addition, time-lapse geophysical measurements together with geotechnical monitoring reveal additional information and are valuable for geotechnical process control, such as groundwater remediation and ground improvement. Shear-wave velocity, which has a stronger link to geotechnical stiffness property, is now readily measured by MASW. Its applications on assessment of liquefaction potential and ground improvements were quite effective, at least qualitatively. However, MASW is basically a 1-D method and does not provide S-wave velocity image with high spatial resolution. Many limitations and potential pitfalls of geophysical methods exist but are not apparent to end users. They are systematically discussed from an engineer\' s perspective. The non-uniqueness nature and weak link to engineering parameters are common problems of geophysical methods. Reasonable inversion results should be obtained with sufficient a priori information and proper initial models. More conclusive or quantitative engineering interpretation can be achieved by data fusion, time-lapse measurements, and physics-based quantitative modeling. Different assumptions and limitations of investigation depth and spatial resolution are inherent in each geophysical method. They are summarized and made clear to avoid overpromise and over-interpret geophysical results. Some examples of practical countermeasures are illustrated. Finally, researches towards the standardization of geophysical methods are suggested to ultimately promote their widespread use in engineering community. Although successful case studies and innovative applications have strengthened the contribution of new geophysical developments to geotechnical problems, several challenges are identified for more common practice of geophysical surveys in engineering applications from an engineer\'s perspective. These include the lack of standard in data reduction, non-uniqueness of data inversion, limitations of exploration depth and resolution, field conditions violating model assumptions, and the weak link between geophysical parameters and engineering parameters. Relevant researches and practical countermeasures regarding these issues are partially discussed herein. More rational and widespread use of geophysics may be realized through the understanding of the limitations and potential pitfalls of geophysical techniques and researches to overcome them.
Applying FDEM, ERT and GPR at a site with soil contamination: A case study
(2015-10-01)
Wang, Tzu-Pin
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Chen, Chien-Chih
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Tong, Lun-Tao
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Chang, Ping-Yu
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Chen, Yi-Chieh
This study employed the combination of three methods, namely the Frequency Domain Electromagnetic (FDEM), Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) to evaluate a heavy-metal contaminated site for both pre- and post-remediation investigations. The main goals were to verify the position and the integrity of the underground storage tanks (UST), and to determine the effectiveness of remediation to ensure no contaminants remained at the site. In general, the GPR survey was effective at locating shallowly buried objects. However, due to the highly conductive nature of the heavy-metal laden sludge, the GPR signals were attenuated severely. Thus, the first attempt to use GPR in the pre-remediation investigation did not achieve the desired results and other methods were deployed. The existence of the UST and the sludge within were confirmed by ERT and the UST shape was mapped by FDEM. The principal remediation scheme was soil replacement by replacing the contaminated soil with clean silt Based on the distinctive property differences of the contaminated soil and the clean silt, the completion of the remediation was confirmed by the differences between pre-remediation and post-remediation in GPR, ERT and FDEM results. (C) 2015 Elsevier B.V. All rights reserved.
Cause and countermeasures for the symmetric effect in borehole-to-surface electrical resistivity tomography
(2018-12-01)
Wang, Haoran
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Lin, Chih-Ping
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交大名義發表
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National Chiao Tung University
Researches and applications of borehole electrical resistivity tomography (BHERT) were mostly about cross-hole ERT (CHERT). Literatures on single borehole-to-surface ERT are limited, although this type of measurement could be useful when only one borehole is available. The undesirable symmetric effect is an important issue in the borehole-to-surface ERT survey. It has been observed that not only the pure in-hole data but also some borehole-to-surface configurations would induce mirrored images in the inversion model. In this study, all the possible borehole-to-surface configurations were classified and investigated for their sensitivity patterns and imaging resolutions, and the root cause of the symmetric effect was revealed to be the condition where one current pole and one potential pole coexist in the borehole. The configurations without symmetric effect suffer from low resolution. The investigation finally led to seeking a balance between resolution enhancement and symmetric effect reduction. Two countermeasures to suppress the symmetrical mirroring were proposed. The combined data inversion approach is based on the capability of each array to resist symmetric effect, while the weighted model stacking technique (WMOST) is derived from the characteristics of inversion models. Both methods were shown to be effective in suppressing the symmetric effect while maintaining sufficient resolution. (C) 2018 Elsevier B.V. All rights reserved.
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
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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.
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.
Dielectric Spectroscopy Using Dual Reflection Analysis of TDR Signals
(2019-03-02)
Ngui, Yin Jeh
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Lin, Chih-Ping
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Wu, Tsai-Jung
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土木工程學系
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Department of Civil Engineering
Time-domain reflectometry (TDR) has been a powerful tool for measuring soil dielectric properties. Initiating from apparent dielectric constant (Ka) measurement up until apparent and complex dielectric spectroscopies, the embedded information in the TDR signal can be extracted to inspire our understanding of the underlying dielectric behaviors. Multiple full waveform inversion techniques have been developed to extract complex dielectric permittivity (CDP) spectrum, but most of them involved prior knowledge of input function and tedious calibration. This rendered the field dielectric spectroscopy challenging and expensive to conduct. Dual reflection analysis (DRA) is proposed in this study to measure CDP spectrum from 10 MHz to 1 GHz. DRA is a simple, robust, model-free, and source-function free algorithm which requires minimal calibration effort. The theoretical framework of DRA is established and the necessary signal processing procedures are elaborated in this study. Eight materials with different dielectric characteristics are selected to evaluate DRA's performance, by using both simulated and experimental signals. DRA is capable of measuring non-dispersive materials very well, whereas dispersive materials require the assistance of a long-time-window (LTW) extraction method to further extend the effective bandwidth. The DRA approach is suitable for field applications that can only record a limited amount of data points and in-situ dielectric spectroscopy.
Dispersion analysis of surface wave testing - SASW vs. MASW
(2017-08-01)
Lin, Chih-Ping
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Lin, Chun-Hung
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Chien, Chih-Jung
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交大名義發表
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National Chiao Tung University
The data reduction method for dispersion relation in surface wave testing is conventionally associated with the certain method of data acquisition, for example, phase shift analysis in the two-station SASW method and 2-D multi-station wavefield transformation of surface wave in the MASW method. The fundamental difference in dispersion analysis between the 2-station and multi-station approach was clarified in this study. Limited to the two channel data, conventional dispersion analysis of SASW suffers from possible phase un-wrapping errors, inefficient data filtering and synthesis, and inability to distinguish multiple modes. The MASW approach, on the other hand, can avoid these problems and provide visualization of dispersion relation through 2D wavefield transformation. As opposed to multiple shots in the SASW testing, the MASW testing typically uses only single shot, limiting the obtainable wavelengths due to near field and far field effects. Combining the merits of these two methods, a multi-shot common receiver configuration survey is proposed to acquire multi-station wavefield for 2D wavefield transformation using as few as two receivers. An additional benefit of the multi-shot common receiver configuration is shown to be better control and higher lateral resolution of the measurement range. (C) 2017 Elsevier B.V. All rights reserved.
Effect of lateral heterogeneity on surface wave testing: Numerical simulations and a countermeasure
(2007-06-01)
Lin, Chih-Ping
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Lin, Chun-Hung
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土木工程學系
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Department of Civil Engineering
The surface wave (S-wave) method has gained popularity in engineering practice for determining S-wave velocity depth profiles. A growing trend is towards the application of S-wave testing for spatially 2-D S-wave velocity tomography, ignoring the assumption of horizontally layered medium. A fourth-order velocity-stress finite difference method is used to perform numerical simulations of S-wave testing in earth models with lateral variation. Results show that the lateral heterogeneity induces a non-stationary property in the space domain, resulting in false depth-related dispersion or higher modes if conventional approach based on stationary assumption is used for the dispersion analysis. Artifacts maybe introduced in spatially 2-D S-wave velocity imaging if the effect of lateral heterogeneity is not accounted for. As a potential countermeasure, a high-lateral-resolution S-wave method is proposed to reduce the effect of lateral heterogeneity while maintaining the resolution and depth range of dispersion analysis. It consists of a walk-away survey and a phase-seaming procedure when synthesizing seismograms with different nearest source-to-receiver offset, allowing wide-wavelength dispersion analysis within a small spatial range. The proof of concept is given with several numerical examples. They show that the high-resolution S-wave method can greatly alleviate the effect of lateral heterogeneity and increase spatial resolution. (c) 2006 Elsevier Ltd. All rights reserved.
Geoelectrical mapping of the Soil and Groundwater Contaminated Site: Case Study from Taiwan
(2016)
Liu, Hsin-Chang
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Lin, Chih-Ping
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Yang, Chieh-Hou
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Wang, Tzu-Ping
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環境工程研究所
In recent years, geophysical technology has been widely used in soil and groundwater investigation and remediation of contaminated sites assessments in Taiwan, such technology can securely work in either small or large sampler areas, and collect data from the traditional one-dimensional data to two-dimensional and three-dimensional data. In other words, geophysical technology helps provide more information to assist the data interpretation, and improves the overall effectiveness of soil and groundwater contamination surveys. Electrical Resistivity Tomography (ERT) is one of useful geophysical technology to the soil and groundwater contaminated sites. By estimating the groundwater flow direction and distribution of contaminations, we could establish monitoring or sampling wells in potential pollution areas. ERT survey could delineate the contaminated areas with high concentrations in relatively simple sites. Even in the seriously DNAPL leakage cases, it is possible to directly detect the DNAPL pool. In this study, we presented the investigation outcomes of electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) at the DNAPLs-impacted site. Evaluation of ERT/GPR technique deployment in detecting buried DNAPLs and assessment of remediation efforts are also discussed. Results indicated zones with anomalously high resistivity to be associated with contaminated DNAPLs presence. Resistivity maps clearly outlined the subsurface distribution and the possible migration path of DNAPLs.
Geotechnical applications and standardization of surface wave method-from engineer's perspective
(2010-01-01)
Lin, Chih-Ping
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Lin, Chun-Hung
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Chang, Tzong-Sheng
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土木工程學系
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Department of Civil Engineering
This paper focuses on the power and concerns of surface wave method in geotechnical applications. It is increasingly used to map not only the vertical variation but also the lateral variation of S-wave velocity. The methods available for surface wave testing and analysis are reviewed and re-examined. Case histories are presented to highlight unique features of surface wave method and point out potential problems. The solution to those problems is proposed and further standardization of surface wave testing is suggested.
High concentration suspended sediment measurements using time domain reflectometry
(2011-04-20)
Chung, Chih-Chung
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Lin, Chih-Ping
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土木工程學系
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防災與水環境研究中心
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Department of Civil Engineering
The existing methods of suspended sediment concentration (SSC) monitoring provide a measurement accuracy significantly influenced by the particle size of suspended sediments, function only under limited measurement range and are not cost effective for field maintenance as well as wide spatial coverage. The paper introduces an innovative SSC monitoring methodology based upon time domain reflectometry (TDR), especially emphasizing on optimum TDR measurement accuracy investigated theoretically and experimentally. Pertinent probe design, probe calibration, as well as data reduction procedures were proposed. Ultimately, the approach can achieve the measurement accuracy to adapt the derived hardware resolution and beyond. In addition, the performance evaluation was carried out considering possible influence factors including water salinity, sediment types and particle sizes, and leading cable lengths. TDR SSC measurements indicate insensitive to sediment particle sizes. After proper calibration, the measurements are also insensitive to water electrical conductivity and not affected by leading cable resistances. There are further advantages of the TDR method including high measurement range from 2 to at least 300 g L(-1), easy calibration, robustness, maintainability, and cost-effective multiplexing. (C) 2011 Elsevier B.V. All rights reserved.
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.