Measurement Method of Thermal Properties of Cementitious Bedding Materials and Unsaturated Soils: Hydraulic Influence on Thermal Parameters

Due to climate-induced variations, changes in the water content of the soil occur, and consequently its hydraulic and thermal properties change as well. Bedding materials for buried energy cables or geothermal installations are usually in capillary contact to the surrounding soil. Thus, they are subject to seasonal changes in the water content caused by natural climatic variations. For the design and construction of structures using thermal energy or dissipating waste heat in the shallow ground, it is important to be able to make reliable forecasts of the thermal and hydraulic properties of partially saturated bedding materials and soils. For this purpose, the climate-related changes of the thermal and hydraulic properties have to be investigated. In this technical note, an experimental setup is described, allowing for the simultaneous measurement of several hydraulic and thermal parameters during dewatering of a specimen. From the data, interrelations between thermal conductivity and water content, water retention characteristics and unsaturated hydraulic conductivity can be derived. This is why, a common evaporation test device was extended using a thermal needle probe. This setup enabled the examination of disturbed and undisturbed soils. A further method, which is also presented in this paper, provides the possibility of investigating cementitious bedding materials in this evaporation test for the first time. This experiment takes only a few days for cementitious bedding materials as well as for undisturbed soil samples. Thus, with only one single experiment, all the basic parameters required for unsaturated hydraulic modeling can be identified. Since thermal conductivity is measured along with the hydraulic parameters, it is possible to assign a value to the thermal conductivity for many hydraulic states of the soil or bedding material.