Deformation and fracture characteristics of rock under creep-impact loading based on subcritical crack growth

During deep resources extraction, deep rock is subjected to high stress and dynamic disturbances, leading to frequent dynamic disasters such as coal rock bursts that severely restrict the safe and efficient production of deep resources. To investigate the deformation and failure mechanisms of deep rock under the combined effects of creep and impact loadings, a rock creep model was established based on subcritical crack growth theory and fracture mechanics. The model provides unified solutions for creep and impact loadings across different strain rate ranges using a unified time scale approach. Additionally, the numerical model for rock under the combined effects of creep and impact was developed using the two-dimensional discrete element software UDEC. Based on the validation of this model, the influence of different creep stress levels and impact loadings on the deformation and fracture characteristics of rock was simulated and studied. The study reveals the following key findings: The rock creep-impact model based on subcritical crack growth theory can effectively describe the three stages of primary creep, steady creep and accelerated creep. The numerical model can accurately simulate the effects of increased creep strain and the shortened time-to-failure in creep after impact loading. As the subcritical crack constant B increases or the stress corrosion index n decreases, the strain rate during the steady creep stage increases, resulting in a shortening of the steady creep stage and the creep failure lifespan. Increasing creep stress levels leads to higher instantaneous elastic strain and the instantaneous strain caused by the same impact loading in the steady creep stage. And the failure time of rock under the action of creep and impact has obvious nonlinear characteristics. With an increase in impact loadings, the instantaneous strain of the rock increases significantly, showing a faster growth rate under high impact loadings. The time-to-failure of the rock varies significantly with changes in impact loading, with a notably shorter time-to-failure under high impact loadings.