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Study on Evaluation of Effective Thermal Conductivity of Unsaturated Soil Using Average Capillary Pressure and Network Model

평균 모세관압과 네트워크 모델을 이용한 불포화토의 유효 열전도도 산정에 관한 연구

  • Han, Eunseon (School of Civil, Environmental and Architectural Engineering, Korea Univ.) ;
  • Lee, Chulho (Geotechnical Engineering Research Division, SOC Research Institute, KICT) ;
  • Choi, Hyun-Jun (School of Civil, Environmental and Architectural Engineering, Korea Univ.) ;
  • Choi, Hangseok (School of Civil, Environmental and Architectural Engineering, Korea Univ.)
  • 한은선 (고려대학교 건축사회환경공학부) ;
  • 이철호 (한국건설기술연구원 SOC성능연구소 Geo-인프라 연구실) ;
  • 최현준 (고려대학교 건축사회환경공학부) ;
  • 최항석 (고려대학교 건축사회환경공학부)
  • Received : 2012.10.05
  • Accepted : 2012.11.28
  • Published : 2013.01.31

Abstract

Thermal conduction of the particulate composites or granular materials can be widely used in porous materials and geotechnical engineering. And it has continued to develop "effective thermal conductivity" of medium by modeling energy relationship among particles in medium. This study focuses on the development of the effective thermal conductivity at the unsaturated conditions of soils using the modified network model approach assisted by synthetic 3D random packed systems (DEM method, Discrete Element Method) at the particle scale. To verify the network model, three kinds of glass beads and the Jumunjin sand are used to obtain experimental values at various unsaturated conditions. The PPE (Pressure Plate Extractor) test is then performed to obtain SWCC (Soil-Water Characteristic Curve) of soil samples. In the modified network model, SWCC is used to adjust the equivalent radius of thermal cylinder at contact area between particles. And cutoff range parameter to define the effective zone is also adjusted according to the SWCC at given conditions. From a series of laboratory tests and the proposed network model, the modified network model which adopts a SWCC shows a good agreement in modeling thermal conductivity of granular soils at given conditions. And an empirical correlation between the fraction of the mean radius (${\chi}$) and thermal conductivity at given saturated condition is provided, which can be used to expect thermal conductivity of the granular soils, to estimate thermal conductivity of granular soils.

입상체의 열전도도 산정에 관한 연구는 다공질 매질이나 지반공학에서 다양하게 사용될 수 있다. 입상체의 열전도도 산정은 입자들 사이의 에너지 관계에 대한 모사를 통해 "유효 열전도도"를 획득하는 것으로 발전하였다. 본 연구는 불포화토의 유효 열전도도를 산정하기 위해 3차원 개별 요소법을 이용하여 입자를 생성하고 기존 네트워크 모델을 수정하여 적용하였다. 수정된 네트워크 모델을 검증하기 위해 3가지 다른 크기의 글라스 비즈와 주문진사를 이용하여 실내시험을 통해 흙-수분 특성 곡선과 포화도에 따른 시료의 열전도도를 산정하였다. 수정된 네트워크 모델에서는 흙-수분 특성 곡선을 사용하여 입자 사이의 평균 유효 열전달 실린더 반경을 조정하고 모델에 적용하였다. 일련의 실내시험과 수정된 네트워크 모델을 사용하여 결과를 비교한 결과, 흙-수분 특성 곡선을 적용한 네트워크 모델은 주어진 불포화 조건에서 입상체 시료의 유효 열전도도를 합리적으로 모사할 수 있는 것으로 나타났다. 또한, 포화상태의 유효 열전달 실린더 반경 계수로 정규화한 예측식을 제안하였다. 제안한 예측식을 통해 기존 네트워크 모델을 사용하여 불포화 상태에서 입상체의 유효 열전도도를 산정할 수 있다.

Acknowledgement

Grant : 주요사업 극한지 지반 안정화 기술 개발 과제

Supported by : 한국에너지기술평가원(KETEP), 한국건설기술연구원

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