Influence of real-time engineering temperature on mechanical behavior and failure mechanism of granite in a tunnel in Southwestern China

Abstract

At present, there is relatively little attention paid to the rock mechanics properties within the engineering temperature range and under small temperature gradients. Combining uniaxial compression tests with particle flow code (PFC) simulations, this study investigates the temperature strengthening mechanism of granite within 20–80 °C. The research reveals a fundamental transition in failure patterns: macroscopic failure modes shift from shear-dominated to tensile-dominated mechanisms as temperature increases, accompanied by microstructural evolution showing smoother fracture surfaces and enhanced intergranular fracture characteristics. Notably, thermal expansion-induced negative strain promotes advantageous strain energy accumulation, which optimizes particle contact relationships and improves frictional properties within the granite matrix. These microstructural enhancements manifest as improved macroscopic mechanical performance, including increased elastic modulus and peak strength, demonstrating a distinctive negative thermal damage phenomenon where moderate heating strengthens rock integrity. A thermal–mechanical-damage statistical constitutive model is developed, with parameter evolution analysis providing mechanistic insights. The findings advance understanding of thermal effects in rock mechanics and offer practical implications for engineering rock mass stability assessment under thermal–mechanical coupling conditions.