<p>Rock engineering stability essentially depends on crack propagation and coalescence, where rock bridge failure often plays a critical role in triggering rock mass engineering disasters. Friction on flaw surfaces significantly affects crack propagation behavior and rock bridge failure, while previous studies have often simplified or directly ignored the influence of flaw surface friction, and have not systematically investigated its coupled effects with rock bridge length on crack propagation and rock bridge failure patterns. In this study, we adopt a novel strength-based fracture method to determine crack propagation direction, which allows for handling contact and friction behavior at flaw surfaces. Fracture behavior in rock specimens containing two parallel closed flaws is systematically modeled under varying friction coefficients and rock bridge lengths. Effects of flaw surface friction and rock bridge length on crack propagation and rock bridge failure patterns are analyzed. Results indicate that during multi-crack propagation, alternating stress release and accumulation at different crack tips cause the propagation process of a single crack to be intermittent rather than continuous. The rock bridge failure pattern exhibits a clear transition with varying friction coefficients, from approximately elliptical shape to linear. Furthermore, we also quantitatively evaluate the influence of flaw surface friction and rock bridge length on crack initiation parameters and analyze the behavior of flaw surfaces during crack propagation. These results reveal the mechanisms by which flaw surface friction and rock bridge length affect crack propagation and rock bridge failure patterns, providing valuable insights for rock engineering stability analysis and disaster prevention investigations.</p>