Investigating soil/pipeline interaction during oblique relative movements

Daiyan, Nasser (2013) Investigating soil/pipeline interaction during oblique relative movements. 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 (11MB)

Abstract

An understanding of the soil restraint on pipelines due to relative pipe/soil movements is important to assess the pipeline's strain response during large ground displacements. The interaction between soil and pipeline can affect serviceability and integrity of pipelines. -- Current engineering practice for pipe/soil interaction is based on an idealized pipeline and soil numerical structural model that evaluates a pipelines mechanical response using beam elements and soil behavior using discrete spring system. The load-displacement relationships are provided in the state of practice for principal directions (i.e. longitudinal, lateral horizontal, vertical upward and vertical downward). -- Recent studies have indicated that in complex pipe/soil relative movements (e.g. axial-lateral or lateral-vertical directions) assuming no interaction among the loads applied to the pipe at different directions is not valid. Therefore, there is a need for more advanced numerical tools and engineering guidelines to assess the pipeline's response in complex loading conditions and reduce technical uncertainty. -- This thesis has investigated the complex soil failure processes and load transfer mechanisms during nonlinear, oblique pipeline/soil interaction events associated with large permanent ground deformations. The oblique loading events considered include combined axial-lateral and axial-vertical (upward) relative pipeline/soil displacements in frictional soils, and lateral-vertical pipeline/soil interactions in both frictional and cohesive soils. -- A series of centrifuge tests of pipelines displaced in a horizontal plane through sand have been conducted for different relative angles between the pipe longitudinal axis and the transverse lateral loading direction. A three-dimensional continuum finite element model was developed using ABAQUS/Standard (Hibbitt et al. 2005) software. The numerical model is validated against experimental results and is used to extend the physical investigation results through parametric studies. -- Interaction diagrams that characterize the coupled soil load-displacement mechanisms were developed and compared with other yield surfaces in the public domain literature. Alternative soil-spring formulations that account for coupled soil deformation mechanisms during oblique pipeline/soil interaction events have been proposed based on interaction diagrams. The effects of this alternative soil-spring formulation on pipelines responses via structural finite element models are shown and discussed in Appendix B of this thesis.

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