Study on rock energy and microscopic failure under different stress states

With the continuous expansion of deep underground engineering, the instability and failure of rock masses during construction have become increasingly prominent. Among these, marble has become a focal point of research due to its widespread occurrence. By integrating laboratory experiments and numerical simulations, this study systematically investigates the mechanical response, the characteristics of energy accumulation and dissipation, as well as fracture and damage evolution in marble. Experimental results demonstrate that increasing confining pressure significantly enhances both the strength and ductility of marble, while the intermediate principal stress exerts a pronounced regulatory effect on its mechanical properties and failure morphology. The stress-strain behaviour and crack evolution under uniaxial, conventional triaxial, and true triaxial loading conditions were simulated using a particle flow numerical method. Energy analysis indicates that tensile failure is the dominant failure mechanism of marble. With increasing confining pressure, the number of bonded damages during failure decreases, the proportion of tensile cracks decreases from about 75 to 61%, while the proportion of shear cracks increases from 25 to 39%. True triaxial numerical simulations further reveal a nonlinear regulatory effect of the intermediate principal stress on energy accumulation and release: a moderate increase enhances rock toughness and delays the peak of energy dissipation, whereas an excessive increase destabilizes energy release and promotes a transition in the failure mode from tensile to combined shear-dominated failure. These findings advance the understanding of failure mechanisms in deep marble and provide a theoretical basis for stability assessment and the development of energy-based criteria in underground engineering.