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Research Papers: Offshore Geotechnics

Two-Dimensional Model for Pore Pressure Accumulations in the Vicinity of a Buried Pipeline

[+] Author and Article Information
H.-Y. Zhao

Griffith School of Engineering,
Griffith University,
Gold Coast Campus,
Gold Coast, Queensland 4222, Australia
e-mail: hongyi.zhao@griffithuni.edu.au

D.-S. Jeng

Professor
Griffith School of Engineering,
Griffith University,
Gold Coast Campus,
Gold Coast, Queensland 4222, Australia
e-mail: d.jeng@griffith.edu.au

Z. Guo

College of Civil Engineering and Architecture,
Zhejiang University,
Hangzhou, Zhejiang 310058, China
e-mail: nehzoug@163.com

J.-S. Zhang

Professor
State Key Laboratory of Hydrology-Water
Resources and Hydraulic Engineering,
Hohai University,
Nanjing 210098, China;
College of Harbor,
Coastal and Offshore Engineering,
Hohai University,
Nanjing 210098, China
e-mail: jszhang@hhu.edu.cn

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received November 12, 2013; final manuscript received May 5, 2014; published online August 4, 2014. Assoc. Editor: Colin Leung.

J. Offshore Mech. Arct. Eng 136(4), 042001 (Aug 04, 2014) (16 pages) Paper No: OMAE-13-1107; doi: 10.1115/1.4027955 History: Received November 12, 2013; Revised May 05, 2014

In this paper, we presented an integrated numerical model for the wave-induced residual liquefaction around a buried offshore pipeline. In the present model, unlike previous investigations, two new features were added in the present model: (i) new definition of the source term for the residual pore pressure generations was proposed and extended from 1D to 2D; (ii) preconsolidation due to self-weight of the pipeline was considered. The present model was validated by comparing with the previous experimental data for the cases without a pipeline and with a buried pipeline. Based on the numerical model, first, we examined the effects of seabed, wave and pipeline characteristics on the pore pressure accumulations and residual liquefaction. The numerical results indicated a pipe with a deeper buried depth within the seabed with larger consolidation coefficient and relative density can reduce the risk of liquefaction around a pipeline. Second, we investigated the effects of a trench layer on the wave-induced seabed response. It is found that the geometry of the trench layer (thickness and width), as well as the backfill materials (permeability K and relative density Dr) have significant effect on the development of liquefaction zone around the buried pipeline. Furthermore, under certain conditions, partially backfill the trench layer up to one pipeline diameter is sufficient to protect the pipelines from the wave-induced liquefaction.

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References

Figures

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Fig. 1

Sketch of wave-seabed-pipeline interactions

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Fig. 2

Mechanisms of wave-induced pore pressures (not in scale)

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Fig. 3

Distribution of vertical distribution of maximum wave-induced oscillatory pore pressure versus relative soil depth. Notation: solid lines = the present 2D model; symbols = 1D experimental results [27], and dashed lines = the analytical solution [3].

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Fig. 4

Verification of the present seabed-pipe model against experimental data in Ref. [28]

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Fig. 5

Comparison of model results with the experiment

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Fig. 6

Comparison of the residual pore pressure between the present numerical model and experimental data [12]

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Fig. 7

The distribution of the initial effective stress near a pipeline after consolidation in seabed

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Fig. 8

Development of liquefaction zone around the pipeline (a) without preconsolidation due to self-weight of a pipeline; and (b) with preconsolidation due to self-weight of a pipeline

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Fig. 9

The distribution of wave-induced residual pore pressure with different initial effective stress conditions at three different locations (black lines (2, −2)—point A, red lines (0, −2.5)—point B, blue lines (10, −2.5)—point C, referring to Fig. 1, see online version for color.). Notation: solid lines = with preconsolidation due to self-weight of a pipeline; dashed lines = without preconsolidation.

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Fig. 10

The distribution of wave-induced residual pore pressure at the bottom of the pipeline for different buried depth (e)

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Fig. 11

Development of liquefaction zone in the vicinity of a buried pipeline (solid lines) and no pipeline (dashed lined) for various buried depth (e)

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Fig. 12

The distribution of wave-induced residual pore pressure at the bottom of the pipeline for various specific gravity of pipeline (γp)

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Fig. 13

Development of liquefaction zone for different specific gravity of pipeline (γp)

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Fig. 14

The distribution of wave-induced residual pore pressure at the bottom of the pipeline for various consolidation coefficient (cv)

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Fig. 15

Development of liquefaction zone for various consolidation coefficient (cv)

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Fig. 16

The distribution of wave-induced residual pore pressure at the bottom of the pipeline for various consolidation coefficient (Dr)

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Fig. 17

Development of liquefaction zone around the pipeline for various soil relative density (Dr)

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Fig. 18

The distribution of wave-induced residual pore pressure at the bottom of the pipeline for various wave height (H), d = 12 m and T = 10 s

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Fig. 19

Development of liquefaction zone in the vicinity of the buried pipeline for various wave height (H)

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Fig. 20

The distribution of wave-induced residual pore pressure at the bottom of the pipeline for various water depth (d)

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Fig. 21

Development of liquefaction zone in the vicinity of the buried pipeline for various water depth (d)

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Fig. 22

The distribution of wave-induced residual pore pressure at the bottom of the pipeline for various wave period (T)

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Fig. 23

Development of liquefaction zone in the vicinity of the buried pipeline for various wave period (T)

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Fig. 24

Wave-seabed-pipe interaction within a trench layer

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Fig. 25

Development of liquefaction zone around the pipeline within the trench soil with various permeability K˜ of the backfill material at different wave cycle. (Hb = B = 1.6 m)

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Fig. 26

Distribution of wave-induced residual pore pressure at the bottom of the pipeline within the trench soil with various permeability K˜. (Hb = B = 1.6 m)

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Fig. 27

Development of liquefaction zone around the pipeline within the trench soil with various relative density D˜r of the backfill material at different wave cycle (Hb = B = 1.6 m)

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Fig. 28

Distribution of wave-induced residual pore pressure at the bottom of the pipeline within the trench soil with various relative density D˜r (Hb = B = 1.6 m)

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Fig. 29

Development of liquefaction zone versus wave cycle with different trench width W (Hb = B = 1.6 m)

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Fig. 30

Distribution of wave-induced residual pore pressure versus wave cycle at the bottom of the pipeline with various trench width W (Hb = B = 1.6 m)

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Fig. 31

Development of liquefaction zone versus wave cycle with different trench thickness B (Hb = B)

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Fig. 32

Distribution of wave-induced residual pore pressure versus wave cycle at the bottom of the pipeline with various trench width B (Hb = B)

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Fig. 33

Velocity field for various thickness of backfill material Hb

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Fig. 34

Development of liquefaction zone versus wave cycle with various thickness of backfill material Hb

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Fig. 35

Distribution of wave-induced residual pore pressure versus wave cycle at the bottom of the pipeline with various thickness of backfill material Hb

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