Advancement of CEL Procedures to Analyze Large Deformation

Abstract Pipeline/soil interaction involves complex interplay of soil type and strength, burial depth, pipeline displacement path, contact mechanics, soil strain localization, and pipe feed-in among other parameters. Further complexity is introduced in fully coupled models to simulate ice keel/seabed/pipeline interaction events for example, where ice keel/seabed interface contact, keel bearing pressures and subgouge soil deformations are important. In order to establish confidence in more complex models, sub-interaction scenarios can be extracted and simplified. This study focuses on pipeline/soil interaction in plane strain form to examine the effects that burial depth and pipe direction of travel have on soil failure mechanisms. The coupled eulerian lagrangian (CEL) method, used in this study, is shown to provide consistent results with past work. The implications of this work in the context of modelling ice keel/seabed/pipeline interaction and model verification are discussed. Introduction Offshore and onshore arctic pipelines are often buried to provide protection from environmental loads, natural hazards and mitigate risk. These pipeline systems may be subject to large deformation geohazards such as ice gouging, frost heave, thaw settlement, seismic fault movement and lateral spreading due to liquefaction. The imposed ground displacement field typically involves large soil deformations and strain based failure mechanisms. Load transfer effects will develop pipe bending and axial feed-in response that may result in significant global and local pipeline deformations. In the past decade, there has been significant development in computational hardware and software technology. This has provided a robust simulation framework to address complex, nonlinear large deformation problems involving contact, material plasticity, strain localization and failure mechanisms. An example of this technology advancement is the Arbitrary Lagrangian Eulerian (ALE) formulation that has been used in the fields of fluid-structure interaction, large deformation solid mechanics and geomechanics [1]. For offshore arctic pipelines, there have been numerous studies illustrating the application of ALE techniques to analyse ice gouge events and assess load effects on buried infrastructure [2–8]. This has provided a more rational basis to address uncertainty and develop practical engineering solutions. The calibration and assessment of these numerical procedures has been primarily based on data from physical models of free-field ice gouge events at 1-g in flume tanks and at higher gravitational fields in reduced-scale centrifuge studies [9–11]. These studies, however, have only examined seabed reaction forces, soil stress and strain field distribution and horizontal subgouge soil deformations. Other factors such as geometric properties of the side and frontal berm, clearing process mechanisms, and vertical and lateral subgouge soil deformation has seen limited assessment [2,8]. Furthermore, the presence of buried infrastructure, such as a pipeline, has a significant influence on the subgouge deformation field and soil strain gradient with depth beneath the ice keel [2]. Consequently, detailed investigations are required to establish confidence in the numerical procedures with respect to data and model uncertainty, and the corresponding relative error. Demonstration of the numerical procedures to adequately simulate nonlinear contact mechanics, interface behaviour, local soil strain gradients, and failure mechanisms with minimal discretization error while maintaining computational efficiency is a demanding technical challenge. In addition, soil constitutive models may need to be improved or developed so that large soil deformation or multi-phase behavior can be simulated.

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