Abstract
Ground improvement has been extensively studied primarily for its ability to enhance mechanical bearing capacity. However, soil stabilization (for strength) often alters thermal properties unpredictably. With the aim to enhance the thermal properties of the soil surrounding the shallow geothermal energy system (SGES) by ground improvement method, this study systematically investigated the thermal properties of kaolin clay, stabilized clay, and thermally enhanced clay. Fundamental thermal properties of kaolin clay were measured under varying moisture contents and porosities, with their linear relationships with the fraction of air established. While stabilization typically reduced soil specific heat capacity due to the conversion of free water into hydration products, this study revealed that cement stabilization created a unique microstructural advantage for thermal conductivity. It was found that the cement-clay at the optimum moisture content exhibited the highest thermal diffusivity. Thermal enhancement of the soils using graphite was the most effective in cement-clay with high moisture content, achieving a maximum increase in thermal diffusivity of up to 189%. Microstructural analysis (SEM-EDS) confirmed that calcium silicate hydrate (C-S-H) gels formed continuous thermal bridges between graphite flakes, effectively mitigating interfacial thermal resistance. These findings provided a theoretical basis for “thermo-active ground improvement”, optimizing heat exchange efficiency in SGES applications.
•Thermal properties of kaolin clay, stabilized clay, and thermally enhanced clay were systematically measured.•The thermal enhancement mechanism of graphite in kaolin clay and stabilized clay were revealed by SEM/EDS.•The feasibility of using the air fraction to predict thermal properties of stabilized clay and graphite-clay was discussed.•Soil treatment recommendations were given to improve SGES heat exchange efficiency.