Natural Densification by Wave Action of Sand Surrounding a Buried Offshore Pipeline

Clukey, Edward C.; Jackson, Christopher; Vermersch, John A.; Koch, S.P.; Lamb, W.C.

doi:10.4043/6151-ms

Cited by 20 publications

(6 citation statements)

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“…For buried offshore pipelines the relative density of the cover material is dependent on the trenching and backfilling processes. Typical pipeline ploughs deposit backfill in a loose to medium dense state , although subsequent wave action can densify the backfill (Clukey et al, 1989). In these loose conditions, it is important to account for the low dilatancy of the backfill.…”

Section: Application To Designmentioning

confidence: 99%

The uplift resistance of pipes and plate anchors buried in sand

2008

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The design of buried anchors and pipelines requires assessment of the peak uplift resistance. This paper describes a limit equilibrium solution for the uplift resistance of pipes and plate anchors buried in sand. The geometry of this solution reflects observations from model tests. Peak angles of friction and dilation are found using established correlations that capture the influence of stress level and density. These angles govern the geometry of the failure mechanism and the mobilised resistance. The solution is validated using a database of 115 model tests on pipes and strip anchors assembled from the published literature. Good agreement with the overall database is shown, without optimisation of any input parameters. The method overpredicts the uplift resistance of smooth model pipes by $10%, highlighting the influence of pipe roughness. In contrast, it is shown that the solution for uplift resistance based on the limit theorems of plasticity is generally unconservative. The assumption of normality, which is required by the limit theorems, leads to an unrealistic failure mechanism involving uplift of a far wider zone of soil than is seen in model tests. Plasticity theory, with normality, is inappropriate for modelling this class of kinematically restrained problem in drained conditions, as normality is not observed. As finite element analysis is not routinely used in practicepartly owing to the difficulty in selecting appropriate input parameters to describe dilatancy and plastic flowthe simple analytical idealisation described in this paper provides a useful tool for uplift resistance prediction. Simple charts for the prediction of peak uplift resistance from critical state friction angle, relative density and normalised burial depth are presented, to aid the design of buried pipes and anchors.

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Section: Application To Designmentioning

confidence: 99%

The uplift resistance of pipes and plate anchors buried in sand

2008

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“…Offshore pipelines have been a commonly used facility for transportation of offshore oil and gas. In addition to construction causes, another key failure mode is the wave-induced seabed instability in the vicinity of pipelines [1,2]. Therefore, the evaluation of seabed stability around the pipeline is one of key factors that needs to be considered in an offshore pipeline project.…”

Section: Introductionmentioning

confidence: 99%

Meshfree Model for Wave-Seabed Interactions Around Offshore Pipelines

Wang

Jeng

Tsai

2019

JMSE

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The evaluation of the wave-induced seabed instability around a submarine pipeline is particularly important for coastal engineers involved in the design of pipelines protection. Unlike previous studies, a meshfree model is developed to investigate the wave-induced soil response in the vicinity of a submarine pipeline. In the present model, Reynolds-Averaged Navier-Stokes (RANS) equations are employed to simulate the wave loading, while Biot’s consolidation equations are adopted to investigate the wave-induced soil response. Momentary liquefaction around an offshore pipeline in a trench is examined. Validation of the present seabed model was conducted by comparing with the analytical solution, experimental data, and numerical models available in the literature, which demonstrates the capacity of the present model. Based on the newly proposed model, a parametric study is carried out to investigate the influence of soil properties and wave characteristics for the soil response around the pipeline. The numerical results conclude that the liquefaction depth at the bottom of the pipeline increases with increasing water period (T) and wave height (H), but decreases as backfilled depth ( H b ), degree of saturation ( S r ) and soil permeability (K) increase.

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“…During installation of offshore pipelines in sand, ploughs deposit backfill soil in a loose to medium dense state (Cathie et al 2005); however, it could be subsequently densified due to environmental loading. For example, Clukey et al (1989) showed that the sandy backfill of a test pipe section densified from relative density (Dr) less than ~57% to ~85-90% in 5 months, which has been attributed to wave action at the test site in the Gulf of Mexico. The uplift resistance offered by soil (Fv) depends on upward displacement (v) and generally comprises three components: (i) the submerged weight of soil being lifted (Ws); (ii) the vertical component of shearing resistance offered by the soil (Sv); and (iii) suction under the pipe (Fsuc).…”

Section: Introductionmentioning

confidence: 99%

Upward Pipe–Soil Interaction for Shallowly Buried Pipelines in Dense Sand

Roy

Hawlader

Kenny

et al. 2018

J. Geotech. Geoenviron. Eng.

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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.

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Natural Densification by Wave Action of Sand Surrounding a Buried Offshore Pipeline

Cited by 20 publications

References 0 publications

The uplift resistance of pipes and plate anchors buried in sand

The uplift resistance of pipes and plate anchors buried in sand

Meshfree Model for Wave-Seabed Interactions Around Offshore Pipelines

Upward Pipe–Soil Interaction for Shallowly Buried Pipelines in Dense Sand

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