A numerical investigation of brittle rock damage model in deep underground openings

The excavation of underground openings generally causes damage to the rock in the vicinity of the openings. The dominant causes of irreversible rock deformations are damage process and plastic flow. Most of the existing elastic–plastic models employed in the analysis and design of rock structures only consider the plastic flow and ignore the full damage process. The common approach used to model the rock failure, does not model the rock realistically and often the important issues such as stiffness degradation, softening, and significant differences in rock response under tensile and compressive loadings are ignored. Therefore, developments of realistic damage models are essential in the design process of rock structures. In this paper, the basic concepts of continuum damage mechanics are outlined. Then, a more clear and accurate definition of the damage function is established. In the definition of rock damage function, many authors considered only the tensile stress condition. Since quasi brittle materials such as rock degrade under tensile and compressive stress fields, separate tensile and compressive damage functions are introduced. The proposed damage functions are formulated in the framework of a damage model which was coded and implemented into a commercial code. Accordingly, the developed algorithm was applied to the simulation of brittle rocks behavior. Using field measurements from the AECL’s (Atomic Energy of Canada Limited) Mine-by Experiment tunnel, the new developed damage model was calibrated and validated for its ability to reproduce the shape and size of excavation damage zone (EDZ) around the Mine-by test tunnel.