Physical and numerical modelling of pipe/soil interaction events for large deformation geohazards

Pike, Kenton P. (Kenton Patrick) (2016) Physical and numerical modelling of pipe/soil interaction events for large deformation geohazards. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Large deformation, differential ground movement events on buried pipelines involve large strain, nonlinear contact interaction, and soil strain localization and failure mechanisms. This study is focused on advancing finite element modelling procedures through laboratory tests to enhance soil constitutive models, physical models to verify simulation tools and algorithms to improve simulation tools that capture realistic behaviour for cohesive and cohesionless soils. The outcomes provide a robust framework for improved confidence in predicted outcomes to support engineering design. The large deformation, ice gouge events, in cohesive soil, and pipe/soil interaction events, in cohesive and cohesionless soil, were simulated using the Coupled Eulerian Lagrangian (CEL) formulation within ABAQUS/Explicit modelling framework. For ice gouge events, the numerical simulation was conducted using total stress analysis and the von Mises yield criterion. The numerical modelling procedures are improved by incorporating the distribution of soil properties, including elastic modulus and shear strength, throughout the domain without the need to develop complex user material subroutines. The numerical predictions were in agreement with available data in the literature and exhibited improved accuracy with respect to the keel reaction forces and subgouge soil deformations. The major contribution was to improve the benchmark and state-of-art for the numerical simulation of ice gouge events in cohesive soil. Having developed confidence in the numerical simulation of large deformation events in cohesive soil, the research focused on advancing the modelling procedures for cohesionless soil. Large-scale, physical tests on lateral pipe/soil interaction events in sand investigated the effects of pipe diameter (254 mm, 609.6 mm), burial depth to pipe diameter ratio (1, 3, 7) and soil density (14.7 kN/m³, 15.6 kN/m³). The main objective was to provide a verification basis for the numerical modelling procedures with respect to the force–displacement response and localized soil failure mechanisms. The physical tests contributed to the limited database, for the range of pipe diameters examined, and the first large-scale lateral pipe/soil interaction tests to provide detailed soil deformation and strain fields using particle image velocimetry (PIV) technique. In parallel with the physical testing program, an enhanced constitutive model for cohesionless soil was advanced through the development of a user-subroutine that accounts for the effects of soil friction angle and dilation angle as a function of plastic shear strain. Laboratory triaxial and direct shear tests were used to characterize the strength parameters. This contribution has practical applications for pipe/soil interaction events in granular soils, particularly at shallow burial depth with low confining pressure, large soil deformations and strains, and dense sand states with strain softening behaviour. Integrating the enhanced constitutive soil models, the numerical modelling procedures, were verified through comparison with the large-scale pipe/soil interaction tests conducted in this study and third-party physical modelling data. An extended study was conducted to assess the verified simulation tool across a range of practical engineering design scenarios. The outcomes from this study illustrated the improved accuracy and confidence in the numerical predictions, based on the tools developed in this study, that provide a significant contribution to the field of buried pipeline design against large deformation ground movement events.

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