Thermo Mechanical and Microstructural Behavior of Clay Soil Under Elevated Temperatures with CBR Prediction Modelling

Perusomula Hemanth, S Krishnaiah

Abstract: This study investigates the influence of thermal treatment on the engineering behaviour, mineralogical structure and bearing resistance of a natural clay soil heated up to 600 ?C. Comprehensive laboratory testing including Atterberg limits, Proctor compaction, direct shear and soaked CBR was conducted to quantify changes in consistency, density, shear strength parameters and penetration resistance. Results indicate a significant reduction in plasticity and cohesion with temperature, accompanied by a progressive increase in friction angle from 26.1? to 46.1?. The soaked CBR improved markedly from 2.5% for untreated soil to 21.4% for thermally treated soil at 600 ?C, demonstrating enhanced load bearing capacity. XRD analysis confirmed the dehydroxylation of kaolinite and breakdown of illite, while SEM images revealed a clear transition from a dense clay fabric to a fragmented granular microstructure, explaining the shift from cohesive to frictional behaviour. Micro structure analysis supported the observed mineralogical transformation with moderate oxide redistribution. A polynomial prediction model (R? = 0.98) was developed with Python (numPy and Pandas libraries) to estimate CBR at intermediate temperatures, incorporating a 95% confidence interval for reliability. Overall, the study provides a mechanistic understanding of how thermal exposure alters the microstructure and geomechanical performance of clay, offering valuable insights for applications involving fire-affected soils, thermal remediation and high temperature geo thermal material processing.

Keywords: thermal treatment of clay, micro structural transformation, high temperature soil behavior, bearing resistance