Elasto-plastic Analysis On Deformation Of Suction Anchor Foundations In Soft Clays Under Cyclic Load

In order to ensure the offshore platform working normally and maintain its safety and stability, the suction anchor foundations undertake not only the working load induced by the upper structure, but also the cyclic load produced by wind, wave, etc. So the assessment on deformation instability process of suction anchor foundations under both static load and cyclic load is necessary.Based on an incremental elasto-plastic boundary constitutive model which can reflect the undrained stress strain response of saturated soft clay under cyclic load, a sub- incremental explicit integration scheme was established by the euler tangent algorithm. Aiming at the characteristics of no elastic region and no yield surface in the boundary constitutive model, modification on traditional sub- incremental explicit integration was made: return the attempted stress state to the boundary surface, instead of returning the attempted stress state to the yield surface for there being no yield surface in the boundary surface model with no e lastic region, enhancing the applicability of the explicit integration algorithm on boundary surface model; determine the Loading and unloading state by the angle between the direction of the attempted stress increment and the outside normal direction of image stress point on the boundary surface, instead of the relative position between the attempted stress point and the yield surface for there being no yield surface in the boundary surface model with no elastic region, to determine the position of the mapping centre. Further, the user material subroutine(UMAT) on the ABAQUS platform was used and a subroutine code which can reflect the undrained stress strain response of saturated soft clay under cyclic load was programmed. Combined with the incremental so lver of ABAQUS platform, an incremental elasto-plastic finite element method that can analyze the deformation of saturated soft clay under both static load and cyclic load by tracing cyclic load varying with time was formed. Cyclic t riaxial tests and cyclic torsion tests were predicted by the finite element analysis and the result was compared with theoretical results based on the constitutive mentioned above, verifying that the incremental elasto-plastic finite element method in the ABAQUS environment was correct.The incremental elasto-plastic finite element analysis method was used to simulate the model test of suction anchor foundations under both static load ing and cyclic loading. The result showed that the inclined cyclic accumulated displacement and the inclined cyclic displacement of the suction anchor obtained by the finite element method in both horizontal and vertical destruction modes approached the result obtained from the model test; a comparison between the horizontal and vertical cyclic accumulated deformation of the suction anchor obtained by finite element method and the model test was made, showing that the result obtained from FEM was smaller, but had the same trend with the model test. So the finite element method can predict the deformation instability process of the suction anchor foundations under both static load and cyclic load to some extent.