Numerical investigation of wave-induced local scour around two pipelines incorporating the effects of the seabed seepage

• Wave-induced seepage substantially enhances scour around twin pipelines. • Seepage enhances scour near the upstream pipeline but is weaker for the downstream. • The scour increases with KC; the upstream-downstream differences decrease at high KC. • Soil permeability affects the scour more significantly than saturation variations. • The effect of the soil response on the scour is pronounced for the lower ks and higher Sr. Wave-induced local scour around tandem submarine pipelines poses significant challenges to offshore infrastructure stability. Although existing numerical studies have investigated a single pipeline, the complex interactions between wave-seabed-scour processes in twin-pipeline configurations remain under-explored. In this paper, an integrated computational framework is used within OpenFOAM® (PORO-FSSI-SCOUR model), which combines hydrodynamic model, seabed response and sediment transport, for two pipelines in a tandem arrangement. The present model employs seepage-modified Shields number formulations that incorporate wave-induced pore pressure variations and associated correction factors that affect the incipient motion of the sediment. Systematic parametric analyses are conducted to investigate the effects of the spacing ratio ( G / D = 1–4), the KC number ( KC = 5–15), the permeability of the soil and the degree of saturation on the evolution of the scour. The results indicate that the inclusion of seabed seepage tends to enhance sediment mobilisation and accelerate scour development compared to conventional approaches. The period-averaged correction coefficient ( R ) consistently exceeds unity, suggesting an increasing role for seepage in sediment transport. The depth of scavenging increases with increasing KC , while the difference between the upstream and downstream pipelines decreases at higher values of KC . In general, soil permeability exerts a more pronounced influence on scour patterns than saturation variation, particularly under low-permeability conditions where enhanced seepage gradients may promote erosion.