Nonlinear Numerical Analysis Of Offshore Structure Failure Due To Seabed Liquefaction Induced By Wave Loading

The analysis for dynamic stability of seabed or offshore foundation under wave loadingis of practical significance in the design and construction of offshore and coastal structures.When waves propagate over the ocean surface, a sequence of wave pressure is induced on theseafloor. The wave pressure induces a stress field and associated pore water pressurefluctuations within the seabed. With the developments of excess pore pressures and thediminishment of effective stresses, part of the seabed may become unstable or even liquefied.The instability of the seabed has been responsible for the damage and destruction of offshorestructures. So it is of theoretic importance and applied value in engineering to research on thedynamic responses of seabed under wave loadings.A cyclic elastoplastic constitutive model, proposed by Oka based on modified flow ruleand the nonlinear kinematic hardening rule, is adopted here to describe the stress-strainrelationship of the seabed soil under wave loading. The governing equations of finiteelement-finite difference coupled method in u～p form are established basing ongeneralized Biot's theory of dynamic consolidation and the cyclic elastoplastic model. Thedynamic equations are solved by Newmark-βtime integration scheme. By simulatingdynamic response of seabed with different terrains under various wave loadings, how theliquefaction and the failure of seabed occur are obtained.Firstly, by analyzing the dynamic response of seabed under wave loading at some depthbelow the sea surface, feasibility of the method is verified. Two wave parameters, waveperiod and water depth, are discussed and dynamic property related of seabed is summarized.Furthermore, the flow deformations of seabed after liquefaction are also obtained bysimulating the seabed with gentle slope.Subsequently, dynamic response of seabed with structure on top is analyzed and thefailure of structure due to seabed liquefaction induced by wave loading is simulated. Thesettlement of the structure and the deformation of the seabed are obtained. By dealing with thecalculated figures, the interface of the structure and the rubble mound is found to be thesection with the biggest liquefied depth.