Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Variations of Complex Permittivity due to Water Content and Heavy Metal Contamination

함수비와 중금속 오염도에 따른 유전상수의 변화

  • Oh Myoun-Hak (Research institute of Energy and resources, Seoul Nationl Univ) ;
  • Kim Yong-Sung (School of Civil, Urban & Geosystem Engrg., Seoul National Univ) ;
  • Yoo Dong-Ju (School of Civil, Urban & Geosystem Engrg., Seoul National Univ) ;
  • Park Jun-Boum (School of Civil, Urban & Geosystem Engrg., Seoul National Univ)
  • Published : 2005.07.01
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Abstract

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.

지반오염조사에 대한 유전상수 측정기법의 적용성을 평가하기 위하여 함수비와 중금속 오염도에 따른 흙의 유전특성 변화를 분석하였다. 유전상수의 실수부와 허수부 모두 체적함수비에 따른 증가경향을 나타내었으며, 특히 MHz 범위에서 유전상수 실수부는 쌍극자모멘트에 비례하기 때문에 흙의 유전상수는 체적함수비에 따른 선형적인 증가경향을 나타내었다. 중금속 용액은 50 kHz 이하의 저주파영역에서 전극분극효과에 의해 농도 증가에 따라 유전상수 실수부가 증가하였으나, 고주파 영역에서는 이온의 수화작용에 의한 물분자의 배향분극 발현의 감소로 인하여 감소하는 경향을 나타내었다. 유전상수 허수부는 중금속 농도 증가에 따라 전도손실의 증가에 의하여 모든 주파수 영역에서 증가하는 경향을 나타내었다. 흙과 중금속 혼합시료의 경우 함수비가 큰 시료에서는 중금속 용액 자체의 유전특성이 그대로 발현되었으나, 함수비가 작은 시료에서는 공간전하분극의 영향이 우세하여 유전상수 실수부가 $10-20\%$정도 증가하는 경향을 나타내었다. 유전상수 허수부의 경우에는 중금속 농도 증가에 따른 뚜렷한 증가경향을 확인할 수 있었다. 본 연구의 결과에 의하면 중금속의 오염감지에 대해서는 유전상수 실수부보다는 허수부의 적용성이 높은 것으로 나타났으며, 현장에서의 정확한 오염도 평가를 위해서는 함수비에 대한 평가가 선행되어야 할 것으로 판단된다.

Keywords

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