Experimental study of heat and moisture migration in unsaturated soils under thermal boundaries

This paper is performed to study the behavior of heat and moisture migration in unsaturated soils applied in geotechnical borehole thermal storage systems. Based on a one-dimensional experimental setup, the dynamic variations of the soil temperature and moisture content under different heat source temperatures and initial moisture contents were measured using the technique of frequency domain reflectometer. The results showed that under a high heat source temperature, the coupling of heat and moisture occurred easily in those soils with a high hydraulic conductivity. As the heat source temperature increased, the soil temperature profile deviated gradually from the linear values predicted by the theory of heat conduction. Both the soil temperature and the moisture content in the vicinity of heat sources appeared an interesting peak phenomenon varying in time and space field. For fine sand under the heat source temperature of 60-80°C, the peak of the moisture content occurred mostly in the range of 4-20% of saturation, where the peak temperature tended to appear earlier than the peak moisture content, depending on the heat source temperature and the initial moisture content. The present results can provide further insight to the complex coupled process of heat and moisture during the migration in unsaturated soils. © 2015 ejge.