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오명학,김용성,박준범,유동주 한국지반공학회 2005 한국지반공학회논문집 Vol.21 No.5
Laboratory experiments were performed to examine the effects of water content and to see if permittivity had sufficient sensitivity to identify subsurface contamination. Both real and imaginary permittivities of unsaturated sand were strongly governed by the volumetric water content. Especially, a linear relationship between real permittivity and volumetric water content was derived at high frequencies (MHz ranges). Heavy metals in pore fluid result in significant increases in the effective imaginary permittivity, due to ionic conduction, but decreases in the real permittivity arises due to the decreased orientational polarization of water molecules caused by hydration of ions. Clear increase in the effective imaginary permittivity with heavy metal concentration was found to be valuable in the application of electrical methods for detecting heavy metals in the subsurface. However, because the permittivity is primarily dependent on the volumetric water content of soil, pre-evaluation on the volumetric water content is required.
Complex Permittivity of Sand at Low Frequency
오명학,김용성,박준범,윤현석,Oh Myoung Hak,Kim Yong Sung,Park Jun Boum,Yoon Hyun Suk Korean Geotechnical Society 2005 한국지반공학회논문집 Vol.21 No.2
본 연구에서는 저주파수 영역에서 유전상수 측정시 발생할 수 있는 왜곡효과를 규명하고, 함수비에 따른 사질토의 유전상수 변화를 실수부와 허수부를 구분하여 조사하였다. 축전기 형태의 셀에서 유전상수를 측정하는 경우 100kHz 이하의 주파수 영역에서 전극분극효과에 의하여 실제 매질의 유전상수보다 크게 측정되었기 때문에 전극 분극효과에 의한 영향을 배제하기 위해서는 100kHz 이상의 주파수에서 유전상수가 평가되어야 하는 것으로 판단되었다. 함수비에 따른 사질토의 유전상수를 평가한 결과 체적함수비 증가에 따라 연속적인 증가경향을 나타내었다. 이는 유전상수 실수부의 경우에는 사질토에서 발생하는 분극이 단위체적당 쌍극자 모멘트에 비례하기 때문이며, 유전상수 허수부의 경우에는 함수비 증가에 따른 전도손실량이 증가하기 때문이다. 그러나 유전상수 실수부에서의 체적함수비에 따른 증가경향은 공간전하분극의 영향이 크지 많은 1MHz 이상의 주파수 영역에서 유효한 것으로 나타났다. This study was performed to identify the presence of measurement distortions such as electrode polarization and to investigate the influence of soil water content on complex permittivity at low frequency. In low frequency measurement using two-terminal electrode system, electrode polarization effect was observed at frequencies less than approximately 100 HBz. The analysis for real permittivity should be performed at frequencies above 100 kHz in order to exclude electrode polarization effect in the analysis of real permittivity at low frequency measurements. For a given soil, both of real and effective imaginary permittivity of wet soil increased continuously with volumetric water content. This is evidenced by the facts that the real permittivity is proportional to the number of dipole moments per unit volume and effective imaginary permittivity is effected by the conduction due to water. However, proportional relation between real permittivity and volumetric water content is valid at upper MHz frequencies.
흙-벤토나이트월에 대한 전기전도도 모니터링 기법의 적용성 평가
오명학,유동주,김용성,박준범 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.7
In this study, applicability of electrical conductivity monitoring technique for containment barrier such as soil-bentonite wall was evaluated. Laboratory tests including permeability tests and column tests were performed to understand variations in electrical conductivity at different bentonite contents, hydraulic conductivities, and heavy metal concentrations. The electrical conductivity of compacted soil-bentonite mixtures was found to increase proportionally with bentonite content. Accordingly, the hydraulic conductivity of compacted soil-bentonite mixtures which decreases linearly with increasing bentonite content was found to have an inversely proportional relationship with the electrical conductivity. In column tests, electrical conductivity breakthrough curves and concentration breakthrough curves were simultaneously obtained. These results indicated that electrical conductivity measurement can be an effective means of detecting heavy metal transport at the desired locations within barriers and verifying possible contaminant leakage. Experimental results obtained from this study showed that the electrical conductivity measurement can be a promising tool for monitoring of containment barrier.
지반 오염도 조사를 위한 전기비저항/정전용량 측정콘의 적용성 평가
오명학,김용성,박준범 한국지반공학회 2006 한국지반공학회논문집 Vol.22 No.7
Resistivity cone penetrometer test (RCPT) can be employed at a relatively low cost for in-situ delineation of subsurface contamination. While the resistivity measurement has a potential to investigate the subsurface contamination, resistivity measurements alone will lead to some degree of ambiguity in the results. In this study, capacitance measurement was incorporated into the RCPT to overcome the ambiguity inherent in electrical resistivity measurements. This study is focused on verifying the applicability of resistivity and capacitance measurements of CPT module to provide information on subsurface contaminated by heavy metal and petroleum hydrocarbon. Laboratory model tests were performed to evaluate the sensitivity of the measured resistivity and relative capacitance on the water content and different types of contaminants. Test results show that simultaneous measurement of electrical resistivity and capacitance can give more reliable information on subsurface contamination. Electrical measurements of the CPT module showed high applicability to be used in detecting saturated soils contaminated by heavy metal and diesel plume floating above the groundwater table.