Micromechanical damage modelling in UDEC software environment for the analysis of rock behaviour under open micro cracks conditions

Nonlinear and unrecoverable rock behaviour under loading is relevant to nucleation, growth and propagation of micro cracks in rock called the damage process. The phenomenological methods have always been used to investigate the rock damage process. In this research, the micromechanical damage model was implemented as it relates microscale and macroscale rock behaviours more efficiently. In this paper, dilute & Mori-Tanaka distribution schemes of micro cracks were introduced, investigated and compared with each other. The micromechanical damage models based on dilute and Mori-Tanaka distribution schemes under tensile stress field (open micro cracks) were formulated. These formulations of micromechanical damage models were coded in C⁺⁺ environment. Then, the DLL file of the developed micromechanical constitutive model was implemented as a new constitutive model in UDEC software. For practical application and verification of the developed model, a reported uniaxial tensile strength test of a granite rock was selected as a basis. The geometry and boundary condition was simulated as closely possible to the real strength test. This reported tensile strength test was modelled by the proposed micromechanical damage model based on the dilute and Mori-Tanaka homogenization schemes. According to the findings, the Mori-Tanaka based micromechanical damage model can simulate the nonlinear rock behaviour especially from beginning of the damage to the peak strength in closer correlation with experimental data. However, the dilute based damage model cannot simulate the nonlinear rock behaviour because it does not take into account the high values of damage variables. Furthermore, the Mori-Tanaka damage model based on decreasing resistance function can simulate nonlinear rock behaviour in better agreement with experimental data. The simulation results of Mori-Tanaka damage model based on incremental resistance function especially in peak strength range were not correlated well with experimental data.