Accurate prediction of burial depth and suspended length for oil and gas pipelines crossing rivers is critical for ensuring structural integrity. Systematic flume experiments were employed to examine local scour under varying hydrodynamic conditions, emphasizing relationships between scour hole expansion rate and flow velocity, water depth, and pipe diameter. Bedload transport predominantly governs riverbed evolution and scour hole development. Larger pipe diameters significantly reduce scour hole formation beneath the pipeline. Vertical expansion rate peaks immediately upon initial erosion, then progressively declines due to canalized flow, while cumulative scour depth continues increasing. Vertical dynamics at the pipe bottom conform to a first-order dynamic response equation, yielding a normalized time-dependent scour depth equation. Ultimate scour depth is collectively influenced by hydraulic parameters, pipe diameter, and sediment characteristics. Dimensionless correlations among scour depth, relative sediment size, and Froude number (Fr) were established via Gauss–Seidel iteration. Horizontal expansion exhibits distinct regimes: single-phase dominates at Fr > 0.6, whereas a secondary phase emerges at Fr ≤ 0.6. Integrating experimental data with empirical vertical expansion models, we propose a comprehensive horizontal scour expansion calculation model. These findings provide substantive insights into scour evolution mechanics and directly inform safety assessments for river-crossing pipelines.
Yang et al. (Mon,) studied this question.