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 offshore platforms in the Gulf of Mexico. The retired platforms are converted to artificial reefs by laying them down on their sides. In the toppling process, the soil resistance on structural members is important as it controls how deep the structure will be settling into the seafloor. The Coupled Eulerian-Lagrangian (CEL) technique in Abaqus/Explicit was used to estimate the soil resistance on tubular members and piles loaded to very large displacements into the marine clays. Horizontal tubular members were pushed vertically to more than 10 times their diameters into the marine clays to model jacket legs penetrating into the seafloor. Pile sections were loaded laterally to more than 5 times their diameters to estimate the large-displacement lateral soil resistance in the upper portion of the piles. Abaqus/Explicit CEL technique is robust and efficient in the numerically challenging, large-deformation finite element analyses. Benchmark analyses were performed to validate the CEL analysis results in a uniform soil profile with published analytical, numerical, and experimental results. The benchmarked CEL models were then modified to include a typical Gulf of Mexico soil profile, where the undrained shear strength and Young’s modulus of clays increase with depth. Two approaches were used to define the depthvarying soil properties in the finite element model: a) an industrystandard approach by discretizing the marine clays into several layers with uniform properties within each layer and b) a more refined approach using a single soil layer with continuous and gradual increase in soil properties with depth. The results from the CEL analyses using the layered soil profile exhibited significant numerical noises, which were greatly reduced by the use of continuous soil profile. The CEL technique can be a powerful tool for other large-displacement soilstructure interaction analyses, such as jack-up spudcan penetration, pipeline embedment/trenching and lateral buckling analyses.