Variation of thermal properties with water content and density of residual and basaltic sands from Chile

Renewable energy has become a relevant alternative to solve energy and environmental problems worldwide. The characterisation of the geothermal resource is fundamental for an efficient and sustainable extraction of heat. In this study, thermal conductivity λ , volumetric heat capacity C and thermal diffusivity α of two soils from Chile, namely Bío Bío sand and Maicillo residual soil, are analysed. Bío Bío sand is a uniform and clean sand which is mainly constituted by basaltic particles, whereas Maicillo is a silty and clayey sand with a high content of quartz. Samples were tested with a thermal needle probe at varying water content and density. Measurements to obtain λ , C and α were undertaken. These results allowed the study of patterns and relationships between geotechnical and heat transfer parameters. It was found that dry soil conditions led to the lowest values of λ , whereas saturated soil conditions led to the highest values. Moreover, Maicillo has higher capabilities to transfer heat than Bío Bío sand, which can reach up to 50% in λ for dense soil and saturated conditions. This is due to its quarzitic and clayey mineralogy and non-uniform grain size distribution. The results from this research represent an important contribution for industrial applications.