Objective Gas transmission pipelines are continually exposed to geohazards such as landslides, subsidence, and flood-induced disasters, resulting in significant risk. Unlike other geohazards, flood-induced disasters involve a multi-stage soil-water coupling process. Continuous water scouring of the surrounding soil can cause irreversible damage to the pipeline. This study analyzes the mechanisms and patterns of pipeline damage caused by flood-induced disasters, aiming to clarify their dynamic evolution, improve safety assessment under soil-water coupling, and enhance disaster prevention for gas transmission pipelines.

Methods A pipe-soil model addressing riverbed downcutting from floods was developed based on a real pipeline project, employing computational fluid dynamics and the discrete element method as the underlying computational framework. The Fluent and Rocky modules in ANSYS were used to simulate riverbed downcutting and investigate its formation mechanism. Numerical simulations captured the evolution of the pipe-soil structure under rapid water scouring, expanding the numerical analysis of flood impacts. A fluid-structure interaction method was applied: flow field parameters for flood scenarios were determined, converted into specific load types using mechanical formulas, and incorporated into pipeline stress analysis. Pipeline reliability under riverbed downcutting was evaluated using the Monte Carlo sampling algorithm.

Results Continuous water scouring caused the pipeline to transition from a fully buried state to an exposed state with an increasing exposed area, and finally to a suspended state when sediment was completely eroded. In the buried and exposed states, the pipeline’s maximum equivalent stress remained low, and the reliability was high based on the failure function. In the suspended state, the maximum equivalent stress increased significantly, leading to reduced pipeline reliability.

Conclusion The fluid-structure interaction simulation combined with Monte Carlo-based reliability analysis offers an innovative approach to studying the complex evolution during flood-induced disasters and provides effective guidance for evaluating pipeline stability under such conditions. However, actual data on flood-induced disasters remain scarce, with most parameters approximated through simulations and lacking robust experimental validation for accuracy.