Deformation and damage properties of rock-like materials subjected to multi-level loading-unloading cycles

In the process of engineering construction such as tunnels and slopes, rock mass is frequently subjected to multiple levels of loading and unloading, while previous research ignores the impact of unloading rate on the stability of rock mass. A number of uniaxial multi-level cyclic loading-unloading experiments were conducted to better understand the effect of unloading rate on the deformation behavior, energy evolution, and damage properties of rock-like material. The experimental results demonstrated that the unloading rate and relative cyclic number clearly influence the deformation behavior and energy evolution of rock-like samples. In particular, as the relative cyclic number rises, the total strain and reversible strain both increase linearly, while the total energy density, elastic energy density, and dissipated energy density all rise nonlinearly. In contrast, the irreversible strain first decreases quickly, then stabilizes, and finally rises slowly. As the unloading rate increases, the total strain and reversible strain both increase, while the irreversible strain decreases. The dissipated energy damage was examined in light of the aforementioned experimental findings. The accuracy of the proposed damage model, which takes into account the impact of the unloading rate and relative cyclic number, is then confirmed by examining the consistency between the model predicted and the experimental results. The proposed damage model will make it easier to foresee how the multi-level loading-unloading cycles will affect the rock-like materials.