Prediction Model for Maximum Scour Depth around Suspended Pipeline under Flood Conditions

Abstract Understanding the evolution of the riverbed around suspended pipelines under unsteady flow conditions is critical for ensuring pipeline safety and mitigating flood-related damage. A physical model experiment was conducted to investigate the changes in the riverbed near underwater crossing pipelines and their effects on pipeline structural stability. The test examined the influence of hydrodynamic conditions, sediment particle size, and pipeline dimensions on local erosion processes. The results indicate that under steady flow conditions, the riverbed evolves through three stages: scour pit formation, pipeline suspension, and scour stabilization. When flood conditions occur, the pre-existing scour equilibrium is disrupted, and the riverbed undergoes three additional stages: flood impact, scour pit expansion, and scour equilibrium. Key factors, including particle size, flow rate, and pipeline dimensions, significantly influence both the duration of bed erosion and the maximum scour depth at the pipeline base. A power-law relationship was established between the maximum scour depth and these governing parameters. Furthermore, based on the effect of pipeline diameter, the Lacey formula was revised to more accurately predict the maximum scour depth. This revised formula provides valuable insights into the safe operation of underwater pipelines under flood conditions.