Numerical modelling of wave-current-seabed-pipeline system: pore pressure dynamics and pipeline stability in liquefiable seabed

Seabed liquefaction under wave-current loading critically threatens submarine pipeline stability. Current-induced wave modifications alter the oscillatory wave pressure imposed on the seabed surface, driving disparities in seabed responses compared to wave-only conditions. These dynamic boundary conditions govern liquefaction progression through seepage processes driven by pore pressure gradients. Existing studies on soil–structure interaction (SSI) within wave-current-seabed-pipeline (WCSP) systems typically adopt third-order wave-current solutions as boundary conditions, which rely on a simplified theoretical framework for wave-current interaction. This framework could induce deviations in seabed boundary conditions and consequently in response predictions. Therefore, this study establishes a numerical solution modifying wave parameters under wave-current interactions based on conservation laws of fluid motion and employs this to develop a wave pressure solution for enhanced boundary conditions. Integrating this wave-current coupling solution, Biot's consolidation theory, and the CycLiqCPSP constitutive model within a coupled numerical modelling system, this research investigates the WCSP system response. The numerical model is validated through published experimental benchmarks. Employing this framework, the study systematically investigates dynamic SSI by analysing seepage forces, progressive liquefaction, and pipeline uplift under varying wave-current coupling scenarios. The results reveal that SSI significantly modifies the liquefaction pattern around pipelines. Specifically, liquefaction initiates beneath the pipeline and gradually extends circumferentially, with buoyant uplift triggering instability once the liquefied zone fully encircles the structure. While currents do not alter this fundamental spatial pattern of wave-induced liquefaction, they exert a pronounced influence on the progression rates. These findings collectively demonstrate a critical link between pipeline stability and the spatiotemporal evolution of seabed liquefaction. Consequently, this study establishes that a comprehensive consideration of wave-current coupling is indispensable for accurate pipeline stability assessment.