Development of a Damage Model for Rock Materials Under Compressive and Tensile Stress Fields

摘要

With increase in depth and size of underground openings, the extent of damage zone around these structures grows and becomes major safety and design issues. The dominant causes of irreversible deformations are plastic flow and damage process. Most of the existing elastic-plastic models employed in the analysis and design of underground structures only consider the plastic flow and not the full damage process. In order to realistically modeling the rock damage process, the important issues such as stiffness degradation, dilatation, softening, anisotropy, and significant differences in rock response under tensile and compressive loadings must be considered. Therefore, developments of realistic damage models are essential in the design process of underground structures. In this paper basic thermodynamic arguments and the general formulation of elastic-degrading material are outlined. Then, a more clear and accurate definition of the damage resistance function and its hardening and softening law are established. In the definition of damage yield function, many authors considered only the tensile microcracking (mode Ι). Since quasi brittle materials such as rock degrade under compressive and shear microcracking (mode Π), separate positive and negative yield functions are introduced. Accordingly, two different algorithms are proposed to evaluate the damage associated with compressive and tensile loadings. The computational algorithm of the developed constitutive model is presented at the end.