TY - JOUR

T1 - Scale dependency of anisotropic thermal conductivity of heterogeneous geomaterials

AU - Li, Kai Qi

AU - Chen, Qi Min

AU - Chen, Guan

N1 - Funding Information: Open Access funding enabled and organized by Projekt DEAL. This research is supported by the National Natural Science Foundation of China (grant No. U22A20596) and International Joint Research Platform Seed Fund Program of Wuhan University (grant No. WHUZZJJ202207). Guan Chen would like to thank the financial support of Sino-German (CSC-DAAD) Postdoc Scholarship Program.

PY - 2024/2/16

Y1 - 2024/2/16

N2 - The precise determination of subsurface thermal properties is critical for ground-source heating systems. The geomaterials are inherently heterogeneous, and their thermal conductivity measured in laboratory and field tests often exhibits anisotropic behaviours. However, the accurate measurement of thermal responses in geomaterials presents a challenging task due to the anisotropy’s variation with the observed scale. Hence, a numerical method is developed in this work and illustrated by taking a typical anisotropic structure of geomaterials with the porosity of 0.5 as an example. The differences in data from laboratory measurements and field tests are discussed to explore the scale effect on anisotropic thermal properties. A series of simulation tests are conducted on specimens with varying dimensions using the finite element method. Results indicate that the thermal properties show a substantial sensitivity to the observation scale, the variation of which decreases with the sample dimensions. By comparing in situ data and laboratory results, the values of average thermal conductivity and corresponding anisotropy ratio are lower than those at small scales, indicating that careful consideration should be given to the thermal properties to account for heterogeneity and anisotropy. In addition, four upscaling schemes based on the averaging method are discussed. This study sheds light on the gap between the laboratory results and the field’s inherent properties and provides guidelines for upscaling small-scale results to field-scale applications.

AB - The precise determination of subsurface thermal properties is critical for ground-source heating systems. The geomaterials are inherently heterogeneous, and their thermal conductivity measured in laboratory and field tests often exhibits anisotropic behaviours. However, the accurate measurement of thermal responses in geomaterials presents a challenging task due to the anisotropy’s variation with the observed scale. Hence, a numerical method is developed in this work and illustrated by taking a typical anisotropic structure of geomaterials with the porosity of 0.5 as an example. The differences in data from laboratory measurements and field tests are discussed to explore the scale effect on anisotropic thermal properties. A series of simulation tests are conducted on specimens with varying dimensions using the finite element method. Results indicate that the thermal properties show a substantial sensitivity to the observation scale, the variation of which decreases with the sample dimensions. By comparing in situ data and laboratory results, the values of average thermal conductivity and corresponding anisotropy ratio are lower than those at small scales, indicating that careful consideration should be given to the thermal properties to account for heterogeneity and anisotropy. In addition, four upscaling schemes based on the averaging method are discussed. This study sheds light on the gap between the laboratory results and the field’s inherent properties and provides guidelines for upscaling small-scale results to field-scale applications.

KW - Anisotropy

KW - Heterogeneous geomaterials

KW - Scale dependency

KW - Statistical volume element

KW - Thermal conductivity

KW - Upscaling method

UR - http://www.scopus.com/inward/record.url?scp=85185219172&partnerID=8YFLogxK

U2 - 10.1007/s10064-024-03571-7

DO - 10.1007/s10064-024-03571-7

M3 - Article

AN - SCOPUS:85185219172

VL - 83

JO - Bulletin of Engineering Geology and the Environment

JF - Bulletin of Engineering Geology and the Environment

SN - 1435-9529

M1 - 73

ER -