Abstract: The rock-concrete interface represents a crucial weakness in engineering structures, substantially impacting their overall structural integrity and stability. To accurately capture the natural roughness of the rock-concrete interface, we developed numerical models of rock-concrete composite Brazilian disk specimens, incorporating randomly generated rough interfaces using the cohesive zone model (CZM). The validity of our method was confirmed through Brazilian splitting tests conducted at various loading angles. Additionally, we investigated the impact of interface roughness and loading angle on the peak load and failure modes of the specimens. The results reveal three typical failure patterns under different loading angles: interface debonding, composite failure, and tensile cracking across the interface of both materials. The mechanical behavior of the specimens is significantly influenced by the loading angle below 70°, whereas its impact becomes negligible above this threshold. The effect of interface roughness on the specimens varies with the loading angle. Specifically, within the range of 15° to 65°, an increase in interface roughness significantly enhances the peak load, improving the bearing capacity of the rock-concrete structure. The failure pattern of the specimens is dictated by the differences in stress states at the interface. A rough interface, however, enhances the bonding and interlocking effect between concrete and rock, influencing the failure pattern. These findings offer deeper insights into the failure mechanisms at the rock-concrete interface and provide valuable implications for engineering applications.

Key words: interface roughness, joint roughness coefficient, Brazilian splitting, digital image correlation, cohesive element