This study investigates the effects of thermal treatment on the mechanical behavior of highly compressible Pak Phanang clay, a soft soil with low strength that typically requires advanced ground improvement methods. Heating is considered a promising technique for enhancing foundation stability, particularly for critical infrastructure. The research focuses on the thermo-mechanical behavior of the clay, emphasizing consolidation and solidification processes that influence load-bearing capacity. Isotropically consolidated undrained triaxial tests were conducted at temperatures of 30 °C, 40 °C, 50 °C, and 60 °C with over-consolidation ratios (OCR) of 1, 2, 4, and 8. The results showed that increasing temperature significantly enhanced both peak deviator stress ( \({q}_{u}\) ) and the secant Young’s modulus ( \({E}_{50}\) ), with a strong linear correlation: \({E}_{50}=108.70\times {q}_{u}\) . Dry density increased and organic matter content slightly decreased under thermal treatment, particularly in normally consolidated clay. Excess pore water pressure (EPWP) increased linearly with temperature across all OCR values. Consolidation volume change also increased with temperature but decreased as OCR rose. The coefficient of consolidation ( \({C}_{v}\) ) improved with temperature, leading to faster consolidation, especially in normally consolidated specimens. The coefficient of permeability ( \(k\) ) increased with temperature but declined with higher OCR, with k rising by 14.6%–24.2% from 30 °C to 60 °C in normally consolidated samples. Predictive models for \({q}_{u}\) and \(k\) based on temperature and OCR demonstrated high accuracy. Overall, the findings provide a reliable understanding of the thermal–mechanical response of this clay type, supporting its application in temperature-assisted ground improvement.
