Evolution mechanism and quantitative characterization of initial micro-cracks in marble under triaxial compression

The initial micro-cracks affect the evolution characteristics of macroscopic deformation and failure of rock but are often ignored in theoretical calculation, numerical simulation, and mechanical experiments. In this study, we propose a quantitative analysis model to investigate the effects of initial micro-cracks on the evolution of marble deformation and failure. The relationship between the micro-crack propagation and the marble failure characteristics was comprehensively studied by combining theoretical analysis with a micro-computed tomography (micro-CT) scanning technique. We found that with the increase of confining pressure, the matrix elastic modulus of the marble first increased and then tended to be stable, while the micro-cracks increased exponentially. The sensitivity ranges of the marble sample matrix elastic modulus and micro-cracks to confining pressure were 0–30 MPa and 30–50 MPa, respectively. The porosity and Poisson’s ratio decreased exponentially. The increasing proportion of internal micro-cracks led to an increase in the sample non-uniformity. The samples presented mainly shear failure under triaxial compression, and the failure angle decreased linearly with the increase of confining pressure. The convergence direction of cracks decreased gradually. This quantitative analysis model could accurately portray the relationship between the overall macroscopic deformation and the deviatoric stress of the samples at the compaction and the linear elastic stages, thus deepening the understanding of the stress–strain behavior of rocks.