简介：Theinitiationofpipelinespanninginvolvesthecouplingbetweentheflowoverthepipelineandtheseepage-flowinthesoilunderneaththepipeline.Thepipelinespanninginitiationisexperimentallyobservedanddiscussedinthisarticle.Itisqualitativelyindicatedthatthepressure-dropinducedsoilseepagefailureisthepredominantcauseforpipelinespanninginitiation.Aflow-pipe-seepagesequentialcouplingFiniteElementMethod(FEM)modelisproposedtosimulatethecouplingbetweenthewaterflow-fieldandthesoilseepage-field.Acriticalhydraulicgradientisobtainedforobliqueseepagefailureofthesandinthedirectiontangenttothepipe.Parametricstudyisperformedtoinvestigatetheeffectsofinflowvelocity,pipeembedmentonthepressure-drop,andtheeffectsofsoilinternalfrictionangleandpipeembedment-to-diameterratioonthecriticalflowvelocityforpipelinespanninginitiation.Itisindicatedthatthedimensionlesscriticalflowvelocitychangesapproximatelylinearlywiththesoilinternalfrictionangleforthesubmarinepipelinepartially-embeddedinasandyseabed.