Failure mechanism and safety assessment method of buried RC pipelines under rockfall impact

China's South-to-North Water Diversion Middle Route project (SNWDP) crosses a geologically vulnerable transition zone between the nation's second and third topographic terraces, where elevation differentials exacerbate slope instability and rockfall hazards. Buried reinforced concrete (RC) pipelines in this area face structural risks when rockfall impact energy surpasses the load-bearing capacity of the pipe-soil system, yet critical knowledge gaps remain regarding impact thresholds and dynamic response mechanisms. Through integrated full-scale field experiments and ANSYS/LS-DYNA simulations, this study systematically investigates (1) dynamic response patterns and (2) safety thresholds for RC pipelines subjected to rockfall impacts. Field testing revealed two key phenomena: localized residual stresses develop in soil near impact zones, while horizontal-dominated soil vibrations induce circumferential strain concentration in pipeline mid-sections. Numerical modeling further uncovered diameter-dependent mechanical responses: peak particle velocities concentrate at pipe waists, whereas maximum principal strains and stresses localize at crown and invert positions, respectively. By correlating tensile stress criteria with energy-impact relationships, we established critical collapse thresholds for Groove-and-Tongue (GT) RC pipelines (90–135 cm inner diameters) under rockfall impacts ranging from 0.1 to 1 m³. These validated safety parameters, expressed as maximum allowable drop heights, provides actionable guidelines for the safety rating of buried pipelines in topographically complex areas.