The Effect of Unloading Path on the Time-Dependent Behavior of Beishan Granite

Abstract

Abstract Understanding the time-dependent characteristics of Beishan granite after excavation is critically important for the long-term stability and disaster control of the high-level radioactive waste repository. In this context, a series of creep tests under different unloading paths are designed to simulate the time-dependent behavior of rock mass after excavation. Results show that the instantaneous volume deformation under each loading step is greatly influenced by the unloading path. Moreover, the unloading path has minor effects on the creep strain. The axial and lateral creep strain is dominated by creep fracture potential, which can be characterized by a unified time-dependent fracture potential index (ξTFPI) for different stress states. It is observed that the creep strain generally increases with increasing ξTFPI. In order to describe the fracture mechanism during the creep process, a damage mechanical model based on time-dependent subcritical crack growth theory is adopted. It reveals that the strain hardening behavior dominates the granite creep process, and the strain softening effect is gradually strengthened with increasing ξTFPI.