ABSTRACT The heat conductivity and diffusivity as well as the hydraulic properties of unconsolidated rocks are important parameters to quantify the conductive and convective heat transfer in the subsurface. Depending on the type and way of installation of an underground heat exchanger system the involved soil undergoes compaction, change in saturation e.g.. The most soil properties will be changed somehow, just the grain size distribution remains constant. In the operation phase the temperature and saturation are variable in time and space. The change in the ratios of the gas phase and water phase in the subsoil affects the themo-physical performance. The hydraulic conductivity of soils is a non-linear function on the water content. The heat capacity of unconsolidated rocks can be calculated from the heat capacities of the individual components and their volume fractions. In contrast, there is no linear dependence of the thermal conductivity and the water content. Established computational models provide approximations for the thermal conductivity as a function of water content and other constraints such as temperature. However, for the additional determination of convective transport behavior, the unsaturated hydraulic conductivity and water retention function, largely dependent on the tortuosity of the pore space, have to be determined simultaneously. Here, for the integrated study of soil mechanics, hydraulic and geothermal properties of unconsolidated rocks, a heat and temperature conductivity meter has been developed and patented. The device allows measurements of samples either under constant pressure of up to 7.6 Mpa which means soil compaction can be varied stepwise or it can be driven at a constant sample volume. The treatment temperatures of the soil samples can be varied from -10 to +80 ° C. Additionally to the parameters such as temperature, pressure, volume and water content, the capillary tension is recorded during the measurement. For the simultaneous study of water transport characteristics and the unsaturated conductivity of undisturbed unconsolidated rock samples, an evaporation test has been developed. It is equipped with a full-space line source to determine the thermal conductivity. This allows the simultaneous measurement of thermal conductivity, water retention characteristics and hydraulic conductivity of a soil sample up to the air entry point of the ceramic tensiometer cap (approx. -780 hPa). The functionality of the equipment and methods has been validated and the devices were used for soil investigation in numerous projects. Determination of the design parameters of shallow geothermal systems and of the heat transfer of burried cables is thepurpose of the methods presented in this study. The data compile mathematical models for the thermo-physical parameters of soils. A mathematical function for calculating the thermal conductivity in dependence of the capillary tension is introduced here and the test results of geotechnical and geothermal soil parameters of sand, clay and silt are presented
