Effects of Multistage Geotechnical Erosion on Dynamic Mechanical Response of Buried Pipelines

River‐spanning pipelines are prone to serious hazards during flooding events, which can trigger erosion, exposure, and large‐scale flotation. In this research, a numerical simulation framework was developed using smoothed particle hydrodynamics (SPH) to analyze the dynamic behavior of pipelines subjected to dam‐breach flood scenarios. The simulation was realized through secondary development based on the Abaqus platform. Key analyses focused on the evolution of hydrodynamic loads—including pressure and force—under different scour angle conditions while also incorporating the roles of varying flood depths and baseline water levels. The study further explored the transient impact phenomena and fluid–structure interaction, benchmarking simulation results against conventional pipeline design standards. Findings demonstrated that hydrodynamic pressure escalates as the scour angle increases and that pipeline response is notably influenced by changes in the initial water level. However, when the dam‐breach flood depth becomes larger, its additional effect tends to taper off if the wave height remains fixed. To address transient impacts and fluid–solid coupling effects more effectively, an amplification method is recommended for use in practical assessments. Complementary pseudostatic analysis was also performed to track the initiation and progression of plastic hinges in simply supported pipelines under flood‐induced forces. Finally, experimental wave flume testing was conducted to validate the fidelity and applicability of the proposed SPH modeling strategy.