Insight into the transition from diffuse microcracking to localized macrocracking in saturated quasi-brittle media: Micro-poromechanics-based approach and analytical solutions

Abstract

In this paper, a new micro-poromechanics-based approach is developed for modeling progressive failure process in saturated quasi-brittle media (SQBM) under compression-dominating stresses. The emphasis is put on the transition from diffuse microcracking to localized macrocracking by incorporating poromechanical interaction. A micro-poromechanical model is first established for the description of diffuse damage and frictional sliding of microcracks by combining linear homogenization and irreversible thermodynamics. In particular, the concept of effective stress in the context of damage mechanics is revisited. The role of fluid pressure in cracking process is clarified. The onset of localized macrocracking is then described as stemming from the coalescence of microcracks when the diffuse damage density parameter reaches a critical value. After that transition point, the dissipation process in the SQBM is primarily attributed to the evolution of localized cracks. Within this frame, an anisotropic poromechanical model is developed for modeling the growth and frictional sliding of oriented localized macrocrack whose orientation is analytically determined and depends on loading path. The displacement discontinuity across the macrocrack can be evaluated. For assessing the performance of proposed approach, a set of examples are examined, including drained and undrained triaxial compression tests. In particular, analytical solutions are obtained and compared with existing experimental data, in terms of stress–strain relations, porosity and fluid pressure evolution, and the transition from diffuse damage to localized cracking.