Finite element (FE) analyses of pipeline–soil interaction for pipelines buried in dense sand subjected to lateral ground displacements are presented in this paper. Analysis is performed — using the Arbitrary Lagrangian–Eulerian (ALE) method available in Abaqus/Explicit FE software — in the plane strain condition using the Mohr–Coulomb (MC) and modified Mohr–Coulomb (MMC) models. The MMC model considers a number of important features and properties of stress–strain and volume change behaviour of dense sand including the nonlinear pre- and post-peak behaviour with a smooth transition and the variation of the angle of internal friction and dilation angle with plastic shear strain, loading conditions (triaxial or plane strain), density, and mean effective stress. Comparing FE and experimental results, it is shown that the MMC model can better simulate the force–displacement response for a wide range of lateral displacements of the pipe for different burial depths, although the peak force on the pipe could be matched using the MC model. Examining the progressive development of zones of large inelastic shear deformation (shear bands), it is shown that the mobilized angle of internal friction and dilation angle vary along the length of the shear band; however, constant values are used in the MC model. A comprehensive parametric study is also performed to investigate the effects of pipeline diameter, burial depth, and soil properties. Many important aspects in the force–displacement curves and failure mechanisms are explained using the present FE analyses.
The uplift resistance is a key parameter against upheaval buckling in the design of a buried pipeline. The mobilization of uplift resistance in dense sand is investigated in the present study based on finite element (FE) analysis. The pre-peak hardening, post-peak softening, and density and confining pressure dependent soil behaviour are implemented in FE analysis. The uplift resistance mobilizes with progressive formation of shear bands. The vertical inclination of the shear band is approximately equal to the maximum dilation angle at the peak and then decreases with upward displacement. The force-displacement curves can be divided into three segments: pre-peak, quick post-peak softening, and gradual reduction of resistance at large displacements. Simplified equations are proposed for mobilization of uplift resistance. The results of FE analysis, simplified equations and model tests are compared. The importance of post-peak degradation of uplift resistance to upheaval buckling is discussed.
Buried pipelines are extensively used for transporting water and hydrocarbons. Geohazards and associated ground movements 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. The pipes are often buried at a shallow depth and therefore the behaviour of soil at low stress level need to be considered for proper modeling of the response of pipelines. In this study, finite element (FE) modeling of pipeline/soil interaction is presented, where the stress-stain behaviour of soil at low stress level is implemented. At first, triaxial test results are simulated to validate the proposed model and numerical techniques. Pipeline/soil interaction in plane strain condition is then simulated for lateral loading. The Arbitrary Lagrangian-Eulerian (ALE) method available in Abaqus/Explicit is used for FE modeling. One of the main advantages of this method is that it can simulate large deformation behaviour. The variation of non-dimensional lateral force with non-dimensional displacement is examined for different depth of embedment of pipeline and soil conditions. Finally, shear band formation in soil due to lateral movement of the pipe is presented.
34The response of buried pipes and vertical strip anchors in dense sand under lateral loading is 35 compared based on finite-element (FE) modeling. Incorporating strain-softening behaviour of 36 dense sand, the progressive development of shear bands and the mobilization of friction and 37 dilation angles along the shear bands are examined, which can explain the variation of peak and 38 post-peak resistances for anchors and pipes. The normalized peak resistance increases with 39 embedment ratio and remains almost constant at large burial depths. When the height of an anchor 40 is equal to the diameter of the pipe, the anchor gives approximately 10% higher peak resistance 41 than that of the pipe. The transition from the shallow to deep failure mechanisms occurs at a larger 42 embedment ratio for anchors than pipes. A simplified method is proposed to estimate the lateral 43 resistance at the peak and also after softening at large displacements. 44Page 3 of 33 (LE) method overpredicts the maximum uplift resistance (mean value) of pipes by 11%, while it 57 underpredicts the anchor resistance by 14%. The authors suggested that this discrepancy might 58 result simply from the feature of the database or be an indication that pipes and anchors behave 59 differently. 60Very limited research comparing lateral resistance of pipes and anchors is available. In a limited 61 number of centrifuge tests, Dickin (1988) showed no significant difference between the force-62 displacement curves for pipes and anchors up to the peak resistance; however, the anchors give 63 higher resistance than pipes after the peak. 64Pipelines and anchors buried in dense sand are the focus of the present study. Anchors can be 65 installed directly in dense sand (Das and Shukla 2013). Buried pipelines are generally installed 66 into a trench. When the trench is backfilled with sand, the backfill material might be in a loose to 67 medium dense state. However, during the lifetime of an onshore pipeline, the backfill sand might 68 be densified due to traffic loads, nearby machine vibrations or seismic wave propagation 69 (Kouretzis et al. 2013). Furthermore, Clukey et al. (2005 showed that the relative density of sandy 70 backfill of an offshore pipe section increased from less than ~ 57% to ~ 85-90% in 5 months after 71 construction, which has been attributed to wave action at the test site in the Gulf of Mexico. The 72 behaviour of buried pipes and anchors can be compared through physical modeling and numerical 73 analysis. Physical modeling is generally expensive, especially the full-scale tests at large burial 74 depths, in addition to having some inherent difficulties, including the examination of the 75 progressive formation of thin shear bands in dense sand. Through a joint research project between 76
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