Effect of temperature on electrical conductivity of soils – Role of surface conduction

Abstract

Temperature has a significant effect on the bulk electrical conductivity (σb) of soils because fluid properties, such as viscosity, which affect σb, are functions of temperature. The governing mechanisms between pore water conduction (Kw) and surface conduction (Ks) in terms of temperature dependency are completely different. Thus, soils with a higher relevance of Ks can exhibit a different temperature dependency of σb when compared to Kw-dominant soils. Therefore, in this study, we aim to determine the temperature compensation parameter (α) of σb of soils as a function of the ratio of Ks to σb. Silica sand and kaolin clay were selected as the Kw- and Ks-dominant materials, respectively. The electrical conductivity of tested materials with varying initial porosities and pore fluid concentrations was measured as a function of temperature in the range of 10 °C to 50 °C. The results of this study showed that Kw-dominant soils have an α value of approximately 2%/°C, whereas the α value of Ks-dominant soils ranges from 1%/°C to 2%/°C as a function of porosity and pore water conductivity. The experimentally determined α value was compared with the α value calculated from the theoretical series–parallel model. Additionally, an empirical model to capture the α value of soils with varying magnitudes of Ks and Kw was suggested. Finally, the suggested model was verified using the results of Korean residual soil (i.e., clayey sand) and two other clayey soils (i.e., kaolin and ca-bentonite clays).