Thermal properties of some Melbourne soils and rocks

The thermal conductivity of soils and rocks is an important property for the design of thermally active ground structures such as geothermal energy foundations and borehole heat exchange systems. This paper presents the results of a laboratory study on the thermal conductivity and volumetric heat capacity of soils and rocks from around Melbourne, Australia. The thermal conductivity and volumetric heat capacity of six soils were experimentally measured using a thermal needle probe and the thermal conductivity of three rock types were measured using a divided bar apparatus. Soil samples were tested at a wide range of moisture contents and densities. The results demonstrated that the thermal conductivity varied with soil moisture content, density, mineralogical composition and particle size and that volumetric heat capacity was strongly dependent on the moisture content of the soils. Rock samples were tested dry and water saturated. Rock samples demonstrated an improvement in thermal conductivity with an increase in density when dry. However, when water saturated, siltstone and sandstone rocks showed no significant correlation between density and thermal conductivity. This was attributed to both variations in mineralogy and anisotropy. The thermal conductivity and volumetric heat capacity data obtained from this study provides an initial dataset of soils and rocks thermal conductivities for the design of thermally active ground structures installed throughout Melbourne, Australia.