Understanding the effect of soil-pipeline interactions in the event of large ground movement is an important consideration for the pipeline designer. Both experimental investigation and computational analyses play significant roles in soil-pipeline research. As part of this effort, a framework incorporating continuum soil mechanics and advanced finite element approach (i.e., ALE and SPH method) for modeling soil pipe interaction was constructed. The overall objective of this work is to develop, validate and apply 3D continuum modeling techniques to assess the performance of pipeline systems subjected to large soil displacements. The numerical models produced may subsequently be used to predict the wrinkle formation and post formation behavior of the pipeline considering the effect of the soil confinement. The aim is to develop a comprehensive wrinkle integrity assessment process. This is the first paper (Part I) in a series of two papers. In this paper a three-dimensional Continuum models using MM-ALE (Multi-material Arbitrary Eulerian Lagrangian) and SPH (smooth particle hydrodynamics) approaches are developed and employed using LS-DYNA. The results are compared with published experimental data of large-scale tests to verify the numerical analysis methods. In the second paper (Part II) the effects of soil restraint on the response of the pipe/soil systems (e.g., pipeline wrinkle and buckle, strain demand) are discussed.
The long linear nature of buried pipelines results in the risk of interaction with a range of geotechnical hazards including active slopes and land surface subsidence areas. Ground movement induced by these geotechnical hazards can subject a pipeline to axial, lateral flexural, and vertical flexural loading. The techniques to predict pipeline displacements, loads, stresses or strains are not well described in design standards or codes of practice. The results of geotechnical site observation, successive in-line inspection or pipeline instrumentation are used to infer pipeline displacement or strain accumulation and these techniques are often augmented through the application of finite element analysis. The practice of using finite element analysis for pipe-soil interaction has developed in recent years and is proving to be a useful tool in evaluating the pipeline behavior in response to ground movement. This paper considers pipeline response to geotechnical hazard-induced loading scenarios related to slope movement transverse to the pipeline axis. The details of the three-dimensional LS-DYNA-based BMT pipe-soil interaction model employing a discrete element method (DEM) are presented in this paper. The validation of the numerical models through comparison with medium-scale physical pipe-soil interaction tests are described to demonstrate that the models are capable of accurately simulating real world events. The models are further calibrated for nominal soil types to replicate the pipe-soil load displacement properties outlined in ASCE guideline recommendations by developing responses that closely agree with these results from the physical trials and engineering judgement. The utility of advanced pipe-soil interaction modelling in supporting strain-based pipeline integrity management or design is demonstrated by presenting the results of geotechnical hazard numerical simulations. These simulations are used to describe the sensitivity of pipeline displacements and strains to the demands of these geotechnical events and develop relationships between the geotechnical event key parameters and pipeline response.
Soil-pipe interactions when large ground movements occur are an important consideration in pipeline design, route selection, guide monitoring and reduce the risk of damage or failure. Large ground movement can be caused by slope failures, faulting, landslides and seismic activities. Such conditions induce large deformations of both the soil and pipe. Analyses of such behavior pose a significant challenge to capabilities of standard finite elements as the capability to analyze large deformations is required. This requirement is difficult to meet for Lagrangian-based code. New developments using ALE methods make it possible to determine soil and pipe deformation confidently for large displacements. This paper describes a study performed to investigate the mechanical behavior of a pipeline subjected to large soil movement. A 3D continuum modeling using an ALE (Arbitrary Eulerian Lagrangian) formulation was developed and run using LS-DYNA. The results are compared with published experimental data of large-scale test to verify the numerical analysis method. The analysis is further extended to analyze the soil-pipe interaction under permanent ground deformation such as those associated with surface fault rupture and landslides.
Pipeline integrity is affected by the action of external soil loads in addition to internal fluid pressure. External soil loads can be generated by landslides or at sites subject to ground subsidence, heave or seismic effects. Under these varied conditions of ground movement potential pipeline safety involves constraints on design and operations. The design processes includes developing an understanding of strains that could be imposed on the pipe (strain demand) and strain limits that the pipe can withstand without failure. The ability to predict the pipeline load, stress or strains state in the presence of soil restraint and/or soil displacement induced loading is not well described in design standards or codes of practice. This paper describes the ongoing work involved in a study investigating the mechanical behavior of buried pipelines interacting with active landslides. Detailed pipe-soil interaction analyses were completed with a 3D continuum SPH method. This paper describes the LS-DYNA numerical modeling process, previously developed by the authors, which was refined and applied to site-specific conditions. To illustrate the performance of the modeling process to consider a translational slide, additional numerical model validation was completed and is described in this paper. These comparisons illustrate that good agreement was observed between the modeling results and experimental full scale trial results. Sample results of the application of the validated 3D continuum modeling process are presented. These results are being used to develop generalized trends in pipeline response to slope movements. The paper describes both the progress achieved to date and the future potential for simplified engineering design tools to assess the load or deformation capacity requirements of buried pipelines exposed to different types of slope movement.
Offshore pipelines in ice environments are increasingly required to operate at higher pressure and temperature conditions. These offshore pipelines can be subjected to stress and strains resulting from loading condition and ice scour created in the area. This paper describes a study performed to investigate the mechanical behavior of High Pressure/High Temperature (HP/HT) pipelines to withstand ice scouring events. A parametric study was completed to define the governing parameters for HP/HT pipeline design. This study was based on 3D continuum modeling with an ALE (Arbitrary Lagrangian Eulerian) formulation that was developed and run using LS-DYNA. The model incorporated large deformation theory, non-linear pipe-soil interaction and non-linear pipe material behavior to define ice interaction induced pipe deformations.
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