Effect of backfilling stiffness and configuration on seabed failure mechanisms and pipeline response to ice gouging

Abstract

Ice gouging is a significant issue for offshore structures in cold environments. Pipelines in Arctic regions are buried in the seabed to prevent the direct contact of pipelines and the impacts of soil displacement from ice gouging. However, choosing the appropriate backfilling material and stiffness to maintain the pipeline's integrity while minimizing construction costs is a complex design consideration. It is crucial to accurately model the interaction between the ice, backfill, trench wall, and pipeline to assess the backfill functionality in a coupled ice gouging analysis. This study comprehensively investigated the effect of backfilling stiffness and configuration on seabed failure mechanisms and pipeline response during ice gouging events on a deeply buried pipeline. The study focused on six different backfill materials, including dense and loose sands and very soft clay to stiff clay. The Coupled Eulerian-Lagrangian (CEL) method was used to simulate the large seabed deformation due to the ice gouging process in a trenched/backfilled seabed in Abaqus/Explicit. Incorporation of the strain-rate dependency and strain-softening effects involved the development of a user-defined subroutine and incremental update of the undrained shear strength within the Abaqus software. Key findings reveal that both overly soft and excessively stiff backfill materials can negatively impact pipeline response during ice gouging. Very soft clay exhibits a distinct "removal" mechanism, leading to increased pipeline displacement, while overly stiff clay and dense sands result in more significant displacement due to efficient force transfer. The results can inform the selection of appropriate backfill materials and backfilling techniques to enhance pipeline protection against ice gouging.