Investigating soil/pipeline interaction during oblique relative movements

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.