Large-Deformation Finite Element Analyses using Coupled Eulerian-Lagrangian Technique for Structural Members Loaded into Marine Clays

摘要

“Rigs-to-Reefs” is one of the options for decommissioning offshoreplatforms in the Gulf of Mexico. The retired platforms are converted toartificial reefs by laying them down on their sides. In the topplingprocess, the soil resistance on structural members is important as itcontrols how deep the structure will be settling into the seafloor. TheCoupled Eulerian-Lagrangian (CEL) technique in Abaqus/Explicit wasused to estimate the soil resistance on tubular members and piles loadedto very large displacements into the marine clays. Horizontal tubularmembers were pushed vertically to more than 10 times their diametersinto the marine clays to model jacket legs penetrating into the seafloor.Pile sections were loaded laterally to more than 5 times their diametersto estimate the large-displacement lateral soil resistance in the upperportion of the piles. Abaqus/Explicit CEL technique is robust andefficient in the numerically challenging, large-deformation finiteelement analyses. Benchmark analyses were performed to validate theCEL analysis results in a uniform soil profile with published analytical,numerical, and experimental results. The benchmarked CEL modelswere then modified to include a typical Gulf of Mexico soil profile,where the undrained shear strength and Young’s modulus of claysincrease with depth. Two approaches were used to define the depthvaryingsoil properties in the finite element model: a) an industrystandardapproach by discretizing the marine clays into several layerswith uniform properties within each layer and b) a more refinedapproach using a single soil layer with continuous and gradual increasein soil properties with depth. The results from the CEL analyses usingthe layered soil profile exhibited significant numerical noises, whichwere greatly reduced by the use of continuous soil profile. The CELtechnique can be a powerful tool for other large-displacement soilstructureinteraction analyses, such as jack-up spudcan penetration,pipeline embedment/trenching and lateral buckling analyses.