Study on strain energy evolution characteristics and mechanisms between two types of fissured granites under true triaxial stresses

This study examines the strain energy evolution processes and the associated failure behaviors of two types of fissured granite under the influence of true triaxial stresses. Strain energy characteristics are critical to comprehending the deformation and failure mechanisms of rock masses. Utilizing Hunan granite as a representative example, this research focuses on the variations in strain energy rate, strain energy conversion rate, and strain energy values at peak strength ( σ p ) across different levels of intermediate principal stress ( σ 2 ). The findings suggest that an escalation of σ 2 enhances the susceptibility of granite to brittle failure. Observations also reveal a reciprocal relationship between the elastic strain energy ( U e ) rate and the dissipated strain energy ( U d ) during the failure process. Within the same σ 2 condition, the U e conversion rate consistently exceeds that of U d prior to reaching crack damage stress. Conversely, beyond this stress threshold, the U d conversion rate consistently surpasses U e , particularly under heightened σ 2 . The study further unveils that at lower σ 2 values, increased dissipated strain energy variation in the σ 2 direction ( U 2d ) results in more pronounced energy dissipation and a higher incidence of cracking on the surfaces of pre-existing fissures. In contrast, at elevated σ 2 values, a reduced U 2d variation corresponds to fewer observed cracks and a greater tendency for the rock to fracture along the minimum principal stress ( σ 3 ) direction. The insights gained from this investigation significantly contribute to the field of rock mechanics, particularly concerning the understanding of true triaxial stress behaviors, and bear vital implications for predicting and ensuring rock stability in engineering practices.