Water retention and thermal conductivity of a natural unsaturated loess

Loess covers large portions of Earth's surface. Loess deposits are typically composed of silt with clay and fine sand particles and usually reach a few meters in thickness. Thermal conductivity of loess varies over a relatively large range from 0·07 to 2 W/(m.K), depending on the particle composition, soil texture and also moisture content. In this study, intact loess was sampled at shallow depth (1 m) in Northern France. Suction, volumetric moisture content and thermal conductivity of soil were measured simultaneously during the application of wetting/drying cycles to the sample. The results show that the volumetric moisture content significantly influences the soil thermal conductivity. As is the case for the water-retention curve, a hysteresis loop can be observed when plotting the thermal conductivity against suction. However, no hysteresis appears when the thermal conductivity is plotted as a function of the degree of saturation.