The effect of pipe-soil interaction on the response of buried pipelines to strike-slip fault

Asgarihajifirouz, Mozhgan (2023) The effect of pipe-soil interaction on the response of buried pipelines to strike-slip fault. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (8MB)

Abstract

Steel pipelines are widely used as a reliable and efficient solution for transmitting oil, gas, water, and other fluids in large quantities. Pipelines are usually buried in the pre-excavated trenches for protection against environmental and functional loads but still threatened by permanent ground displacement caused by geohazards like strike-slip faults. Trenches are usually backfilled with pre-excavated material as the most cost-effective solution. Depending on trenching methodology, environmental loads, and construction strategy, the backfilling material is remolded to different extents. The different stiffness between the backfill and native soil may affect the failure mechanisms of the soil surrounding the pipeline and consequently the pipeline’s structural response in the fault zone. Most of the research that have been conducted on the evaluation of pipeline-soil interaction effect on the pipe response has neglected the pipeline-backfill-trench wall interaction effects by assuming a wide trench filled with a uniform backfill. Therefore, a proper understanding of the pipeline structural response to the fault-induced lateral movement needs a deep understanding of pipeline-backfill-trench wall interaction. The pipeline-backfill-trench wall interaction is usually modelled by performing 2D planar large deformation finite element (LDFE) analysis using coupled Eulerian-Lagrangian (CEL) technic, where the pipe is assumed to be rigid. This approach which is usually enforced to minimize the computational effort downplays the significance of longitudinal structural response of the pipeline. Three-dimensional large deformation modelling of the anisotropic soil surrounding the pipeline along with structural deformations is currently not feasible because of needing extreme computations, difficulties in simulation of ground movement, modelling the multi-contact bodies between the pipe, backfill and trench wall, etc. These difficulties have caused the researchers and engineers to assume a Lagrangian soil domain in 3D analyses and compromise the accuracy of the analysis because of mesh distortion in large deformations. Therefore, there is an industry need for a solution to incorporate the pipeline-backfill-trench wall interaction effects into the 3D analysis of the fault-induced pipeline deformations. In the present study, first the pipeline-backfill-trench wall interaction was incorporated into an analytical pipeline-fault interaction model to examine the strength of analytical methods in implementation of the soil interaction effects. Then a 3D pipeline-fault interaction model was developed using Lagrangian soil domain to investigate the limitations of this approach. Eventually, a new decoupled methodology was developed by combining the advanced continuum modelling of the pipeline-backfill-trench wall interaction using CEL analysis and a 3D beam-spring pipeline model to overcome the aforementioned limitations. The proposed decoupled method comprises to main steps. First a Coupled Eulerian-Lagrangian (CEL) model was used for LDFE analysis of the trenched/backfilled pipeline in a 2D planar fashion to obtain the lateral soil resistance (p-y curves) involving pipeline-backfill-trench interaction effects. Then the extracted lateral soil resistance for various displacements was transferred to a 3D beam-spring pipeline model to obtain the pipeline response to the fault-induced large displacements. The proposed methodology used the accuracy advantage of continuum CEL model with simplicity advantage of beam-spring model to create an efficient tool for incorporation of the pipeline-backfill-trench wall interaction effects into the structural analysis of the pipeline attached by strike-slip fault. Moreover, the results were compared with pre-developed Lagrangian model to assess the improved model performance. The study contributed to a deeper insight into this challenging engineering problem showing the significance of incorporation of the pipeline-backfill-trench wall interaction effects into the structural analysis of pipelines attacked by fault. In addition, the study resulted in developing a set of analysis tools that can be effectively used in daily engineering practice by the pipeline industry.

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