Deformation of trenched multilayer pipelines during large lateral displacement due to subsea geohazards

Abstract

Large lateral displacement of trenched multilayer pipelines may be induced by ground movement, landslides, ice gouging, etc. The significant difference between the shear strength of the backfill material and the native soil may affect the pipeline-backfill-trench interaction, the failure mechanisms, and consequently the lateral soil resistance. However, this challenging and less-explored aspect has not been covered thoroughly in design codes, even for rigid pipes. This paper investigates the influences of multilayer pipeline-backfill-trench interaction on the deformation of pipe section, soil failure mechanism, resultant lateral soil resistance, and soil pressure on the pipe by large deformation finite element analyses. A decoupled model consisting a Coupled Eulerian-Lagrangian (CEL) approach with a rigid pipe in ABAQUS was created along with a finite element (FE) model of multilayer flexible pipe in ANSYS to assess their relative merits for this problem. A parametric study was conducted to investigate the influences of key factors, including the trench geometry, stiffness of backfill material, native seabed soil properties, burial depth, and intensity of pipeline-trench bed interaction. The study showed that the ignorance of the pipeline-backfill-trench interaction by using uniform soil might result in underestimation and overestimation of the lateral soil resistance at different displacement amplitudes.