• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.115-125
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• 2023

In this study, we evaluated the behavior of frozen soil using an electrical resistivity survey method-a nondestructive technique-and examined its characteristics through field experiments. Frozen soil was artificially prepared by injecting fluid to accelerate the freezing process, and naturally frozen soil was selected in a nearby area for comparison. A dynamic cone penetration test (DCPT) was performed to compare the reliability of the electrical resistivity survey, and time-domain reflectometry surveys were performed to assess the moisture content of the ground. Field experiments were conducted in February-when the atmosphere temperature was below freezing-and May-when the temperature was above freezing. This temperature-compensated method was used to determine reliability because the behavior of frozen soil depends on the underlying temperature. In the resistivity survey method, a section of high electrical resistivity was observed under freezing conditions due to the frozen water and converted into porosity. The converted porosity was compared with the porosity inferred from the DCPT, and the results showed that the measured electrical resistivity was valid.

• Computers and Concrete
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• v.31 no.4
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• pp.293-306
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• 2023

This study proposes and demonstrates a smart monitoring system that uses transmission lines embedded in a reinforced concrete structure to detect the presence of defects through changes in the electromagnetic waves generated and measured by a time-domain reflectometer. Laboratory experiments were first conducted to identify the presence of voids in steel-concrete composite columns. The results indicated that voids in the concrete caused a positive signal reflection, and the amplitude of this signal decreased as the water content of the soil in the void increased. Multiple voids resulted in a decrease in the amplitude of the signal reflected at each void, effectively identifying their presence despite amplitude reduction. Furthermore, the electromagnetic wave velocity increased when voids were present, decreased as the water content of the soil in the voids increased, and increased with the water-cement ratio and curing time. Field experiments were then conducted using bored piles with on-center (sound) and off-center (defective) steel-reinforcement cage alignments. The results indicated that the signal amplitude in the defective pile section, where the off-center cage was poorly covered with concrete, was greater than that in the pile sections where the cage was completely covered with concrete. The crosshole sonic logging results for the same defective bored pile failed to identify an off-center cage alignment defect. Therefore, this study demonstrates that electromagnetic waves can be a useful tool for monitoring the health and integrity of reinforced concrete structures.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.300-301
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• 2007

본 논문에서는 실시간 스펙트럼 추정기에 기반하여 시간-주파수 영역 반사파 계측 시스템에서의 동축케이블 결함을 검출하는 방법을 제안한다. 시간-주파수 영역 반사파 계측 시스템은 가우시안 포락선(Gaussian Envelop)모양의 첩 신호를 기준신호로 하여 도선에 반사파를 분석하는 기법으로써 타 방법에 비하여 높은 정확도를 자랑하는 것으로 알려져 있다. 하지만 결함 위치를 추정하기 위해 Wigner 시간 주파수 분포 함수를 이용하므로 계산량 증가에 따른 실시간 구현이 어렵다는 단점이 있었다. 이러한 단점을 극복하기 위하여 본 논문에서는 LMS 스펙트럼 추정기를 이용한 시간-주파수 영역 반사파 계측 시스템의 구현방법을 새롭게 제안한다. 제안된 기법은 실제 동축케이블에 대한 실험결과를 통하여 그 성능을 입증하도록 한다.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.1
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• pp.15-25
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• 2021

In this study, a method of leakage detection was proposed to locate leak position for a reservoir pipeline valve system using wavelet coherence analysis for an injected pressure wave. An unsteady flow analyzer handled nonlinear valve maneuver and corresponding experimental result were compared. Time series of pressure head were analyzed through wavelet coherence analysis both for no leak and leak conditions. The leak information can be obtained through either time domain reflectometry or the difference in wavelet coherence level, which provide predictions in terms of leak location. The reconstructed pressure signal facilitates the identification of leak presence comparing with existing wavelet coherence analysis.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.29-30
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• 2022

The unit-water content has a very significant effect on the durability of the construction structure and the quality of concrete. Although there are various methods for measuring the unit-water content, there are problems of time required for measurement, precision, and reproducibility. Recently, there is an FDR sensor capable of measuring moisture content in real time through an apparent dielectric constant change of electromagnetic waves. In addition, various artificial intelligence techniques that can non-linearly supplement the accuracy of FDR sensors are being studied. In this study, the accuracy of unit-water content measurement was compared and evaluated using machine learning and deep learning techniques after normalizing the data secured in concrete using frequency domain reflectometry (FDR) sensors used to measure soil moisture at home and abroad. The result of comparing the accuracy of machine learning and deep learning is judged to be excellent in the accuracy of deep learning, which can well express the nonlinear relationship between FDR sensor data and concrete unit-water content.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.15-25
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• 2003

Time Domain Refletometry, or TDR, is a remote sensing electrical measurement technique that has been used for many years to determine the spatial location and nature of various objects, especially in the United States of America and Australia at mining industry. Since early on 1990, the TDR techniques have been applied to the geotechnical engineering such as : deformation measurement of rock slope and landslide, monitoring of ground water content and ground water level change, investigation of ground contamination and its movement. The first application of this technique, in 1996, to the domestic area is to determine the possibility of ground settlement caused by subsidence from abandoned underground mines at the Tongri and Gosari in Gangwon-d. In this paper, through the results of analysed deformation data between conventional measurements and the TDR, it was concluded that the TDR technique is a useful instrumentation method for the prediction of ground deformation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.8
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• pp.967-975
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• 2012

This paper presents a method to measure reflection coefficients of microwave devices or antennas based on time domain analysis with sampling oscilloscopes. The reflection coefficients were extracted by the Fourier transformation of echo pulses from devices with respect to the 20 GHz incident pulse signals. The three-error terms, which are commonly used for the correction of a microwave network, were determined using a 3.5 mm calibration kit. In addition, a modified error-correction model associated with a directional coupler for reflection coefficient measurements is introduced. The results were compared with those of measured with a commercial vector network analyzer.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.2
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• pp.110-116
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• 2009

This study was to verify and calibrate seven kinds of soil water sensors for volumetric soil water content(VSWC) measurement under field. Types of sensors were TDR (Time Domain Reflectometry) and FDR(Frequency Domain Reflectometry). Two kinds of TDR were TRIME(profile type), and Mini-TRASE(rod type). Five kinds of FDR were EasyAG, EnviroSCAN, PR-1(profile type), and WET-1(rod type). VSWC by TRIME and Mini-TRASE compared with VSWC by soil core showed the standard error of about 2.4%, and 1.4% which is the smallest value among all the sensors used in the experiment, respectively. The errors of EasyAG and EnviroSCAN analyzed with scaled frequency(SF) were about 2.6%, and 2.8% and those by 1 versus 1 correspondence were about 2.6%, and 2.6%, respectively. WET-1 showed about 2.0% of error, which is the smallest value among errors by FDR sensors. PR-1 with the error of about 4.7% should be hard for application in field. Therefore, users on soil water sensors have to take into consideration the errors of sensors revealed after the calibration for the correct measurement of VSWC in field. The rest except for PR-1 among the sensors could be used for VSWC measurement with 1.4~2.6% error.

• The Journal of Engineering Geology
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• v.13 no.4
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• pp.419-428
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• 2003

In order to evaluate groundwater movement and the infiltration of contaminants, such as petroleum products, the determination of porosity and effective porosity is very important. Porosity and effective porosity are important physical parameters that determine the transfer and movement of water and solutes in porous media. Various methods of determining these parameters have been developed, with varying degrees of accuracy and applicability. Most of the existing methods produce static results. They do not produce instantaneous and real time of porosity and effective porosity in a porous media. In this study, we used a new permittivity method called Frequency Domain Reflectometry with Vector analyzer (FDR-V) to determine the porosity and effective porosity of some sand samples in the laboratory. The advantage of the FDR-V method is that it instantaneously determines the temporal variation of dielectric constants of porous media. Then, the porosity and the effective porosity of porous media are computed using well established empirical equations. Results obtained from the FDR-V method compared favorably with results from other permittivity methods such as gravimetric, injection and replacement tests. The ratio of effective porosity to porosity was 85 - 92 %, when FDR-V was used. This value compared favourably with 90 %, which has been usually quoted in previous studies. Considering the convenience and its applicability, the EDR-V permittivity holds a great potential in porous media and contaminant transport studies.

• Journal of the Korean GEO-environmental Society
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• v.13 no.12
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• pp.17-25
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• 2012

In this study, dielectrical constant of the ground was measured using TDR method and correlated with water contents and density of ground. In order to evaluate the applicability as a cavity exploration, model experiments were carried out to analyze the effects of cavity size on the dielectrical constant. Test result indicated that dielectrical constant of the ground tended to linearly increase with the increase in water contents and density, which can be represented in a certain relational expression. Also, the dielectrical constant of ground varied sensitively with the cavity size of ground. The results conclude that the dielectrical constant, water contents and density of the ground proved to have a correlation among them, and the dielectrical constant is expected to be a basic data on cavity exploration.