Numerical investigation on quasi-dynamic behaviours of fractured rocks under uniaxial compression using new rate-dependent contact models

The behaviour of fractured rocks under quasi-dynamic loads significantly influences the stability of rock engineering projects under dynamic disturbances. To account for strain rate effects, new rate-dependent contact models were proposed in this study. Then, numerical models of fractured rocks were generated for quasi-dynamic simulations under uniaxial compression, aiming to investigate the impacts of strain rate and fracture intensity. The results show that the contact models can effectively replicate the rate-dependent behaviours of uniaxial compressive strength (UCS), and an increasing strain rate would induce a rise in UCS of fractured rocks. Additionally, the number of microcracks initiated in rock matrix and fractures show increasing trends, resulting in the higher number of failure planes and more complex failure patterns as the strain rate increases. In contrast, UCS is negatively correlated with fracture intensity, and the intensity's increase enhances the complexity of failure patterns. Regarding microcracking behaviours, the number of microcracks in rock matrix decreases with increasing intensity, while the number of microcracks within fractures increases. Since the mechanical properties of rock matrix are stronger than those of fractures and the initiation of microcracks requires externally input energy, the variations of microcracking behaviours might be intrinsic mechanisms underlying the changes in UCS.