Natural soil thermal behaviour and site description for the underground thermal energy storage case study

Energy geostructures (EGS) and shallow underground thermal energy storage (UTES) systems are receiving increasing attention from the research community and policymakers thanks to the appealing energy savings that can be achieved and the consequent reduction in energy expenditures and carbon emissions. However, no implementations of EGS with UTES exist in the Czech Republic, neither at the building nor at the district level. This partly stems from a lack of knowledge of the ground response to thermal loading but also from an insufficient understanding of the interaction with other renewable energy sources and the associated challenges. We present site description with its ground and air tempetarure long term trends for a proof-of-concept model demonstrating the feasibility of an implementation of UTES in the Czech Republic. Furthermore, we present detailed soil description, soil mechanical properties and an extensive experimental program conducted under controlled conditions on the selected natural soil – Březno formation marlstones from Dubičná, the Czech Republic – to investigate the influence of temperature on soil compression behaviour. The experimental programme is conducted in an advanced thermo-hydro-mechanical (THM) oedometer cell and involves a series of compression and creep oedometer tests with the range of investigated temperatures between 20 and 60°C. The influence of temperature on both compressibility and the rate of creep deformation will be quantified within the studied temperature range. The experimental data will provide essential input for calibrating advanced coupled THM viscohypoplastic constitutive models, which will be further used in the proof-of-concept model.