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Research Papers: Offshore Geotechnics

Experimental Study of Shaft Resistance of Model Piles in Fluidized and Nonfluidized Fine Sand

[+] Author and Article Information
Larissa de Brum Passini

Associate Professor
Department of Construction Engineering,
Federal University of Paraná,
Curitiba, Paraná 81531-980, Brazil
e-mail: larissapassini@hotmail.com

Fernando Schnaid

Professor
Department of Civil Engineering,
Federal University of Rio Grande do Sul,
Porto Alegre, Rio Grande do Sul 90035-190, Brazil
e-mail: fschnaid@gmail.com

Rodrigo Salgado

Charles Pankow Professor
Civil Engineering,
Lyles School of Civil Engineering,
Purdue University,
West Lafayette, IN 47906
e-mail: rodrigo@ecn.purdue.edu

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 June 13, 2016; final manuscript received March 6, 2017; published online May 25, 2017. Assoc. Editor: Lizhong Wang.

J. Offshore Mech. Arct. Eng 139(5), 052001 (May 25, 2017) (12 pages) Paper No: OMAE-16-1062; doi: 10.1115/1.4036371 History: Received June 13, 2016; Revised March 06, 2017

Torpedo piles installed by dynamic penetration have been used as anchors in the Brazilian offshore oil production infrastructure practice for two decades. Dynamic penetration aided by fluidization of the soil during pile penetration is now being contemplated as a method of installation that would allow deeper penetration. The two key design questions in connection with torpedo piles are how far they penetrate and what their pullout capacity is. In a companion paper, the authors addressed the first question, whereas in the present one the second question is attended through laboratory tests using model piles, essentially pipes simulating torpedo piles without wings. The model piles were installed in two different ways: by fluidization, which enabled the piles to sink by their own weight, and by monotonic jacking. Pullout tests were then performed on the model piles in both fluidized and nonfluidized sandy soils prepared at two initial relative densities. Results from the laboratory tests indicate that shaft uplift capacity of fluidized piles is essentially independent of the sand initial relative density. The measured values of the coefficient of lateral earth pressure (Ks) derived from the fluidized model tests are lower than those reported for other methods of pile installation, in some cases being lower than K0. Finally, the shaft resistance of fluidized piles increases after installation as the soil reconsolidates and particles rearrange.

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Figures

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Fig. 1

Pullout tests in pile installed at (a) fluidized and (b) nonfluidized soil

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Fig. 2

Grain-size distribution of the test sand

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Fig. 3

Schematic representation of the experiment

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Fig. 4

CPT tests carried out in fluidized and nonfluidized sand

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Fig. 5

Typical shaft uplift resistance versus displacement for tensile pile tests in fluidized and nonfluidized sand: (a) full test and (b) enlarged scale

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Fig. 6

Typical pile roughness image from profilometer tests

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Fig. 7

Pile shaft uplift capacity versus pile length in nonfluidized soil at (a) Dr = 50% and (b) Dr = 90%

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Fig. 8

Normalized coefficient of lateral earth pressure versus pile length in nonfluidized soil at (a) Dr = 50% and (b) Dr = 90%

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Fig. 9

Pile shaft uplift capacity versus pile length in fluidized soil: (a) immediately and 4 h after installation and (b) 24 and 48 h after installation

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Fig. 10

Normalized coefficient of lateral earth pressure versus pile length in fluidized soil: (a) immediately and 4 h after installation and (b) 24 and 48 h after installation

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Fig. 11

(a) Schematic representation of the fluidized zones during a typical installation test and (b) test performed next to the tank wall

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