The influence of non-linear stress-strain behavior of dense sand on seabed response to ice gouging

Abstract

Subsea pipelines crossing the Arctic shallow waters are usually threatened by ice scour. A cost-effective solution to physically protect the pipeline against the ice gouging is to bury the pipeline in the seabed. Determining the minimum burial depth to minimize the construction cost and ensure pipeline integrity is a challenging design aspect. This requires proper modeling of the ice keel-soil interaction for an accurate assessment of the subgouge soil deformation and the keel reaction forces in a free field ice gouging analysis. In this study, the ice gouging process in dense sand was simulated by advanced large deformation analyses using Coupled Eulerian-Lagrangian (CEL) approach in ABAQUS/Explicit. A modified Mohr-Coulomb (MMC) model was coded into a simplified user subroutine to incorporate the effect of plastic shear strain accumulation, loading condition, density, and confining pressure on the shear strength parameters of dense sand. The MMC model captured the non-linear pre-peak hardening and post-peak softening of the dense sand that is not modeled by conventional Mohr-Coulomb (MC) model. The existing test results and numerical studies were used to verify the performance of the MMC model in ice gouging analysis. A comprehensive parametric study was conducted to investigate the effect of ice keel configuration and soil model parameters on keel reaction forces, subgouge soil deformations, and the soil berm formations. The proposed model resulted in a more accurate prediction of the seabed response to ice gouging and showed the significance of modeling the strain rate dependency of dense sand in ice gouging analysis. The proposed methodology was found to be a strong but simple framework that can be effectively used in daily engineering practice.