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Safety and Reliability

Influence of Spud-Can-Soil Interaction Modeling and Parameters on the Reliability Index of Neka Drilling Jack-Up Platform

[+] Author and Article Information
M. R. Emami Azadi

 Azarbaijan T.M. University, Tabriz, East-Azarbaijan 51549, Irandr.emami@azaruniv.edu

J. Offshore Mech. Arct. Eng 132(3), 031601 (Mar 17, 2010) (13 pages) doi:10.1115/1.4000399 History: Received September 10, 2008; Revised August 19, 2009; Published March 17, 2010; Online March 17, 2010

In the present study, the influence of spud-can-soil modeling and parameters on the reliability index of jack-up platform is investigated. Neka platform is studied as a case, which is a three-leg drilling jack-up type platform located in water depth of about 91 m in the Caspian Sea region. Various spud-can-soil interaction models such as pinned, fixed-base, hyperelastic, and nonlinear elastoplastic spud-can models are applied. The soil type is varied from loose to dense sand and also from soft NC clay to very stiff OC Clay. The effect of bias and coefficient of variation (COV) of the spud-can-soil interaction modeling and also the soil parameters such as the effective interface soil friction angle and also the undrained shear strength of clayey soil are studied. The results showed that inclusion of spud-can-soil interaction may have a considerable effect on the reliability of the jack-up platform. In particular, the bias and COV of soil have shown to have more significant effect on the reliability of jack-up platform in loose sand and soft clayey type soils. It is also found that bias in strength modeling of jack-up itself has less profound effect on the reliability index of the jack-up-foundation-soil system. Importance factors of spud-can-soil modeling are found to be quite considerable. The key aspect is that the inclusion of jack-up-spud-can-soil interaction is more crucial with respect to the reliability of jack-up platform than the choice of interaction model itself.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

A spud-can footing of jack-up system (after Amdahl (3))

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Figure 2

A FE model of Neka jack-up platform (after Nobari (24))

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Figure 3

A deformed shape of Neka jack-up model in Y-direction (after Nobari (24))

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Figure 4

A FE model of spud-can foundation of Neka jack-up embedded into soil (after Nobari (24))

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Figure 5

A view of (scaled-up) deformed model of spud-can foundation of Neka jack-up embedded into sea-bed

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Figure 6

A deformed shape of spud-can-soil model with corresponding plastic utilization factor (USFOS model)

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Figure 7

Total dynamic and static base-shear versus wave height for the jack-up-spud-can-soil system

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Figure 8

Reliability index of jack-up system variation with the internal soil friction angle (Hs=15.5 m)

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Figure 9

Reliability index of jack-up system versus the internal friction angle of soil (Hs=12.5 m)

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Figure 10

Annual probability of failure of jack-up system variation versus internal friction angle of soil (Hs=15.5 m)

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Figure 11

Reliability index of jack-up system variation with undrained shear strength of soil (Hs=15.5 m)

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Figure 12

Reliability index of jack-up system versus preload factor for medium-dense sand (Hs=12.5 m, Hs=15.5 m)

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Figure 13

Reliability index of jack-up system variation with dynamic base-shear (Hs=12.5 m, Hs=15.5 m)

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Figure 14

Reliability index of jack-up system versus the embedment ratio of the spud-can on soft clay (Hs=12.5 m)

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Figure 15

Reliability index of jack-up system versus COV of internal friction angle of loose sand (Hs=12.5 m)

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Figure 16

Reliability index of jack-up system versus COV of internal friction angle of very loose sand (Hs=15.5 m)

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Figure 17

Reliability index of jack-up system versus COV of internal friction angle of dense sand (Hs=12.5 m)

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Figure 18

Reliability index of jack-up system versus COV of internal friction angle of very dense-sand (Hs=12.5 m)

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Figure 19

Reliability index of jack-up system versus COV of undrained shear strength of soft clay (Hs=12.5 m)

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Figure 20

Reliability index of jack-up system versus COV of undrained shear strength of very soft clay (Hs=15.5 m)

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Figure 21

Reliability index of jack-up system versus COV of undrained shear strength of stiff clay (Hs=12.5 m)

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Figure 22

A three-leg Neka drilling type jack-up platform (12)

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Figure 24

Hardening Law for spud-can model in USFOS (after Amdahl (3))

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Figure 23

Associated and nonassociated plasticity rules for spud-can model in USFOS (after Amdahl (3))

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