Finite element analyses of soil/pipeline interactions in sand with an advanced soil constitutive model

Roy, Kshama Sundar (2012) Finite element analyses of soil/pipeline interactions in sand with an advanced soil constitutive model. Masters 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 (4MB)

Abstract

Inexorable demand of energy intensified the search for oil and gas in remote and harsh regions. The operations related to exploration and production of oil and gas has been increased significantly over the last 30 years. The liquid hydrocarbon and natural gas products are usually transported through pipelines, which traverse large distances through a variety of soils. Failure of such pipelines could cause a significant economic loss and environmental damage. Geohazards and the associated ground movement represent a significant threat to pipeline integrity that may result in pipeline damage and potential failure. Safe, economic and reliable operation of pipeline transportation systems is the primary goal of the pipeline operators and regulatory agencies. Pipelines are usually buried or partially embedded into the seabed. To develop a reliable pipelines design method the complex behaviour of seabed sediment (soil) and soil/pipeline interaction should be properly modeled and analyzed. -- Finite element (FE) modeling has been widely used for predicting the response of buried pipelines. One of the main challenges in FE modeling of buried pipelines is to use appropriate soil constitutive model. Most of the FE analyses used built-in soil constitutive models in available commercial FE software. However, their prediction might be better if an advanced soil constitutive model is used. -- The main objective of this research is to perform finite element modeling for analyzing the response of pipelines buried in sand. The primary focus of this research is to adopt an advanced soil constitutive model which might have a significant impact on pipeline response due to soil movement and to implement it in the commercial finite element software package ABAQUS with a user defined subroutine UMA T. All the analyses presented are in drained condition. -- In this study numerical analyses of soil/pipeline interaction are performed using the built-in Mohr-Coulomb soil constitutive model in ABAQUS FE program. This study shows the limitations and advantages of this constitutive model. Reviewing available soil constitutive models in the literature, it is identified that NorSand soil model proposed by Jefferies (1993) could better simulate the behaviour of sand particularly the dilation under monotonic loading. NorSand soil constitutive model implemented in ABAQUS FE software using user defined subroutine UMA T is used for modeling the response of pipelines under lateral, vertical (upward) and oblique loading events. Finite element analyses are also performed with built-in Mohr-Coulomb model. It is shown that the NorSand UMA T can simulate better the force displacement behaviour including the post-peak softening, which cannot be done with Mohr-Coulomb model with a constant dilation angle. The failure envelope obtained with NorSand UMAT for combined lateral and vertical (upward) oblique loading for a deep burial pipeline in dense sand is comparable with the analytical solution and previous numerical analyses.

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