Investigation on the Effect of Initial Damage on the Time-Dependent Deformation of Rock Materials Under Step Loading

Investigating the creep properties of damaged rocks is essential for evaluating the long-term stability of seismically cracked slopes in earthquake-prone regions. In this study, cyclic loading-unloading and step creep loading tests were sequentially performed on metamorphic sandstone, granite, and phyllite. Dissipated energy was introduced to establish the initial damage model, and the effect patterns and mechanisms of initial damage on creep properties were analyzed. The experimental results showed that dissipated energy and the damage variable increased linearly with the number of loading-unloading cycles. The increase in initial damage results in greater creep strain, higher steady-state creep rate, and increased dissipated energy under the same creep loading, while reducing the long-term strength of the rock. Prior loading-unloading promoted the development of microcracks and accelerated the time-dependent deformation of the rock. This study provides a new understanding of the long-term stability of seismically cracked slopes in strong-earthquake mountainous areas.