Mechanical properties and damage characteristics of phyllite subjected to high-temperature treatment

• The mechanical behaviors and energy characteristics of phyllite under thermal-mechanical action are analyzed. • The effects of temperature and bedding angle on rock strength degradation are discussed. • A segmented damage constitutive model of phyllite after high-temperature is established. Deep engineering often faces high ground temperatures in complex geology. For anisotropic rocks like phyllite under temperature, property characterization and damage constitutive modeling grow complex, further complicated by their intricate anisotropy amplified at high temperatures. In this study, the uniaxial compression tests were performed on phyllite samples with varying bedding angles after exposure to high temperatures in this paper. The results reveal significant anisotropy in strength and deformation. Peak strength and elastic modulus initially decreased then increased with increasing bedding angle, reaching a minimum at 45° Across the 20 °C-600 °C range, these properties generally increased then decreased with temperature, with accentuated anisotropy at higher temperatures. The energy storage limit is minimum at a 45° bedding angle and maximum at 200 °C. A brittle-to-ductile transition was observed with increasing temperature. Finally, a segmented damage constitutive model was proposed, which can effectively capture the damage evolution of rocks during deformation and failure processes. This study provides important reference for the analysis of the failure mechanism of deep underground engineering, especially the temperature effect analysis of layered phyllite.