Travelling wave-induced liquefaction of sand deposits

Abstract

The sea-floor deposit is assumed to be a saturated porous medium modelled by a two-phase system for which the coupled governing equations are derived from the theory of mixture. A constitutive model based on the generalized plasticity-bounding surface formulation is proposed to describe the soil behavior. An artificial boundary is suggested to deal with the unbounded domain problem. Thc coupled governing equations and the material model have been implemented into a nonlinear finite element program to analyze the travelling wave-induced liquefaction of seabed deposits. The rcsults of two case studies are presented. The first case examines the response of sand deposit to the wave train at a site of underwater pipelines for nuclear power plants in Lake Ontario where the deposit was found to vary from loose to medium dense. The second case investigates the sea-floor behavior under a storm wave at the Ekofisk oil tank site in the North Sca where the deposit was reported to be dense. The results agree with the field observations.Ke? ~vorc1.s: seabed instability, liquefaction, finite element, plasticity, sand, cyclic loading, travelling wave, unbounded domain.On a Cmis I'hypothkse que les dCpBts de fond ocCaniq~~e constituent un milieu poreux sature, niodellisC par un systkme a deux phases pour lequel les Cquations principales co~~plCes sont obtenues a partir de la thiorie du melange. Un modkle constitutif base sur la formule gCnCralis6e plasticit&-surface de delimitation est suggCrC pour dCcrire le comportement du sol. Une frontikre artificielle est proposee afin de tenir compte du problkme du domaine illimitC. Les Cquations principales co~~pldes et le modele de materiau ont ete mis en oeuvre sous forme de programme non IinCaire d'CICments finis afin d'analyser la liquefaction des depbts de fond marin provoquee par I'onde progressive. Les rksultats de deux Ctudes de cas sont prCsentCs. Le premier cas examine la rCaction des dCp6ts de sable au train d'ondes sous les pipelines submerges de centrales nuclCaires du lac Ontario oil les dCpBts varient de meubles 2 moyennement denses. Le second cas analyse le co~nportement du fond ocCanique soumis a une onde de temp&te aux installations de stockage dc petrole de Ekofisk, dans la mer du Nord, oh les dCpBts sont denses. Les rCsultats obtenus correspondent ;tux observations in situ.Mots clks : instabilitk du fond ocCanique, IiquCfaction, ClCment fini, plasticite, sable, chargement cyclique, onde progressive. domaine illimitk.[Traduit par la redaction]Can.