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Research Papers: Offshore Geotechnics

Experimental and Numerical Studies of the Excess Pore Pressure Field Surrounding an Advancing Spudcan Footing

[+] Author and Article Information
Jiang Tao Yi

School of Civil Engineering,
Chongqing University,
No. 83 Shabei Street,
Chongqing 400045, China
e-mail: yijt@foxmail.com

Yu Ping Li

Key Laboratory of Geomechanics
and Embankment Engineering,
Ministry of Education;
Geotechnical Research Institute,
Hohai University,
Xi kang Road 1,
Nanjing 210098, China
e-mail: juliya-li@hotmail.com

Yi Wei Li

School of Civil Engineering,
Chongqing University,
No. 83 Shabei Street,
Chongqing 400045, China
e-mail: thxiami@gmail.com

Yu Yang

Department of Civil and Environmental
Engineering,
National University of Singapore,
Blk E1A #07-03, 1 Engineering Drive 2,
10 Kent Ridge Crescent,
Singapore 117576
e-mail: yangyu_fl@bgy.com.cn

Yong Liu

Department of Civil and Environmental
Engineering,
National University of Singapore,
Blk E1A #07-03 1, Engineering Drive 2,
10 Kent Ridge Crescent,
Singapore 117576
e-mail: liuy@nus.edu.sg

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 January 1, 2017; final manuscript received September 30, 2017; published online November 16, 2017. Assoc. Editor: Ioannis K. Chatjigeorgiou.

J. Offshore Mech. Arct. Eng 140(2), 022002 (Nov 16, 2017) (14 pages) Paper No: OMAE-17-1002; doi: 10.1115/1.4038344 History: Received January 01, 2017; Revised September 30, 2017

The rapid jack-in process of spudcan footing tends to generate substantial build-up of excess pore pressure below the spudcan underside. An intimate knowledge of the excess pore pressure concentration is thus of significance for understanding both the short-term and long-term mechanical behavior of spudcan. As yet there is a dearth of information in this area. This paper presents a comprehensive research to explore the pattern and magnitude of the excess pore pressure field surrounding an advancing spudcan. Both centrifuge experiments and effective-stress large deformation finite element analyses (LDFEAs) were involved, while the former served mainly to benchmark the latter and the latter provided a complete information database of the excess pore pressure. The bulb-shaped excess pore pressure concentration zone was identified below the spudcan underside. Sizes of pressure bulbs as well as the magnitudes of excess pore pressures inside them bore close relationship to the penetration depths and soil's properties. The results of parametric study led to the development of a simple yet useful approach to estimate the spudcan-penetration-induced excess pore pressure in soil without carrying out the complicated computation. Necessary charts and tables were provided to facilitate its usage. It is expected that the development of such an approach can aid the practicing engineer to obtain a quick and rough estimate of excess pore pressure generated in the midst of the jack-up spudcan penetration and prepare for its short-term and long-term implications.

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Figures

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Fig. 1

Centrifuge model setup

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Fig. 2

LDFEA model: (a) side view and (b) plane view

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Fig. 3

In situ undrained shear strengths measured during centrifuge flight

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Fig. 4

Spudcan penetration resistance profiles

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Fig. 5

Bearing capacity factors at various depths

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Fig. 6

Measured (PPT-S) and calculated pore pressure variation at the base of spudcan

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Fig. 7

Normalized excess pore pressure (Pn) derived from measured (PPT-S) and calculated pore pressure variation at the base of spudcan

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Fig. 8

Comparison of (a) measured (PPT1) and calculated pore pressure variation inside soil, (b) measured (PPT2) and calculated pore pressure variation inside soil, (c) measured (PPT3) and calculated pore pressure variation inside soil, (d) measured (PPT4) and calculated pore pressure variation inside soil, (e) measured (PPT5) and calculated pore pressure variation inside soil, and (f) measured (PPT6) and calculated pore pressure variation inside soil

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Fig. 9

Excess pore pressure contours: (a) d = 5.3 m/0.44D, (b) d = 7.3 m/0.61D, and (c) d = 9.3 m/0.78D (dots in the graphs denote locations of pore pressure transducers whose measurements at that instant are superimposed below)

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Fig. 10

Normalized excess pore pressure (Pn) contours: (a) d = 6.1 m/0.5D, (b) d = 10.8 m/0.9D, and (c) d = 18.1 m/1.5D

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Fig. 11

Pnr/D curves associated with radial cuts A-1 to A-3 (a) and B-1 to B-3 (b)

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Fig. 12

Variation of (a) coefficient β1 with normalized depth d/D for different κ and (b) coefficient β2 with normalized depth d/D for different κ

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Fig. 13

Effect of M change on the normalized excess pore pressure (Pn) contours (d = 13.3 m/1.1D)

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Fig. 14

(a) Effect of M change on diagonal radial profiles (d = 13.3 m/1.1D) and (b) effect of M change on vertical radial profiles (d = 13.3 m/1.1D)

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Fig. 15

Variation of coefficient α with M

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Fig. 16

Effect of λ change on the normalized excess pore pressure (Pn) contours (d = 13.3 m/1.1D)

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Fig. 17

Effect of κ change on the normalized excess pore pressure (Pn) contours (d = 13.3 m/1.1D)

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Fig. 18

(a) Effect of κ change on diagonal radial profiles (d = 13.3 m/1.1D) and (b) effect of κ change on vertical radial profiles (d = 13.3 m/1.1D)

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Fig. 19

(a) Effect of diameter change on normalized excess pore pressure (d = 1.0D) and (b) effect of shape change on normalized excess pore pressure (d = 1.0D)

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