Deformation and Damage Failure Behavior of Mudstone Specimens Under Single-Stage and Multi-stage Triaxial Compression

In tunnel engineering, due to the effect of excavation disturbance, the surrounding rock mass can produce an excavation damage zone with different damage extents. Therefore, knowledge of rock deformation and damage behavior is especially significant for the design of deep tunnel support. However to date, a few experiments and numerical simulations have been conducted to investigate the deformation and mechanical failure behavior of damaged rocks. Therefore, in this research, multi-stage triaxial compression test was used to investigate the mechanical behavior of mudstone specimens with different damage extents by experiment and two-dimensional particle flow code. First, a group of micro-parameters was calibrated by single-stage triaxial compression experiments of mudstone, and the numerical results agree very well with the experimental results. Then, multi-stage triaxial compression experiment and discrete element modeling of mudstone specimens were carried out. The more axial strain the specimens sustained, the less strength they had (because the degree of damage increased). A damage variable was defined by the ratio of the area of micro-cracks to the total area of the specimen. As the post-stress reducing ratio increases, the damage variable increases rapidly until the post-stress reducing ratio reaches 0.4; then, it remains constant. The force field were analyzed to reveal the damage evolution mechanism in the mudstone specimens under multi-stage triaxial compression.