Investigating thermal effects on physical properties and mechanical behaviour of a dolomitic marble during complete triaxial compression at different scales

High-temperature-induced thermal damage to rocks can significantly affect their physical properties and mechanical behaviour embedded at different depths due to microstructural changes. Although many studies have reported the high temperature effects on the microstructure changes and the corresponding mechanical responses, the coupled effects of thermally induced microstructure changes and confining pressure levels on the complete stress-strain behaviour and the relations between major and secondary failure planes in post-peak response remain poorly understood. In this study, three types of samples were extracted from the same intact block of Beijing dolomitic marble, exposed to different thermal treatments, and subjected to various test programs. Physical properties at particle scale (i.e. particle size distribution and micro-crack development) and element scale (i.e. colour parameter, ultrasonic wave velocity and open porosity), complete stress-strain behaviour at different confining pressures, and post-failure characteristics (i.e. failure pattern, stress-induced cracks and post-failure small particle distribution) were examined. Thermal damage led to the formation of inter- and intra-particle microcracks that increased discontinuities and small particle percentages, hence causing significant changes in the physico-mechanical properties of the marble. While higher temperatures reduced peak stress and Young’s modulus at zero confining pressure, the overall post-failure structural characteristics were found to be more affected by confining pressures, higher confining pressures simplified failure modes and reduced secondary crack formation. Although higher temperatures increased small particle generation, confining pressures notably diminished their quantity during shearing, highlighting the complex interactions between thermal and external stress conditions.