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Ocean Engineering

Undrained Load Capacity of Torpedo Anchors Embedded in Cohesive Soils

[+] Author and Article Information
José Renato M. de Sousa

Department of Civil Engineering, Centro de Tecnologia, COPPE/UFRJ, Bloco I2000, Sala I116, Cidade Universitária, Ilha do Fundão, Rio de Janeiro CEP 21945-970, Braziljrenato@laceo.coppe.ufrj.br

Cristiano S. de Aguiar, Gilberto B. Ellwanger

Department of Civil Engineering, Centro de Tecnologia, COPPE/UFRJ, Bloco I2000, Sala I116, Cidade Universitária, Ilha do Fundão, Rio de Janeiro CEP 21945-970, Brazil

Elisabeth C. Porto, Diego Foppa, Cipriano José de Medeiros

 PETROBRAS Research and Development Center, Cidade Universitária, Quadra 7, Ilha do Fundão, Rio de Janeiro CEP 21949-900, Brazil

J. Offshore Mech. Arct. Eng 133(2), 021102 (Nov 16, 2010) (12 pages) doi:10.1115/1.4001953 History: Received November 30, 2009; Revised April 20, 2010; Published November 16, 2010; Online November 16, 2010

This paper presents a numerical based study on the undrained load capacity of a typical torpedo anchor embedded in a purely cohesive isotropic soil using a three-dimensional nonlinear finite element model. In this model, the soil is simulated with solid elements capable of representing its nonlinear physical behavior and the large deformations involved. The torpedo anchor is also modeled with solid elements, and its geometry is represented in detail. Moreover, the anchor-soil interaction is addressed with contact finite elements that allow relative sliding with friction between the surfaces in contact. A number of analyses are conducted in order to understand the response of this type of anchor when different soil undrained shear strengths, load directions, and number and width of flukes are considered. The results obtained indicate two different failure mechanisms: The first one involves significant plastic deformation before collapse and, consequently, mobilizes a great amount of soil; the second is associated with the development of a limited shear zone near the edge of the anchor and mobilizes a small amount of soil. The total contact area of the anchor seems to be an important parameter in the determination of its load capacity, and, consequently, the increase in the undrained shear strength and the number of flukes and/or their width significantly increases the load capacity of the anchor.

Copyright © 2011 by American Society of Mechanical Engineers
Topics: Stress , Soil
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References

Figures

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Figure 1

Typical torpedo anchor with four flukes: (a) conical tip; (b) top with details of the padeye

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Figure 2

General view of the FE model

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Figure 3

Drucker–Prager and Mohr–Coulomb yield surfaces in the deviatoric plane

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Figure 4

General view of a FE mesh for a torpedo anchor: (a) top and (b) bottom parts of the flukes

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Figure 5

Load application

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Figure 6

FE meshes for the analysis of a torpedo anchor: soil mesh, anchor mesh, and soil mesh previous to the anchor installation

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Figure 7

Details of the FE mesh: (a) surrounding soil and torpedo anchor; (b) surrounding soil and soil within the torpedo anchor location

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Figure 8

Dimensions, in m, of the analyzed torpedo anchor

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Figure 9

Torpedo anchor cross sections: (a) four, (b) three, and (c) no flukes

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Figure 10

Embedment depth versus anchor drop height: torpedo anchor with four flukes

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Figure 11

Load versus normalized displacement curves of a torpedo anchor with four flukes embedded in soil A: loads in plane 1

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Figure 12

Load versus normalized displacement curves of a torpedo anchor with four flukes embedded in soil B: loads in plane 1

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Figure 15

Load capacity versus load inclination curves of a torpedo anchor with four flukes embedded in soils with different undrained shear strengths: loads in plane 1

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Figure 16

Ultimate vertical capacity versus ultimate horizontal capacity of a torpedo anchor with four flukes embedded in soils with different undrained shear strengths: loads in plane 1

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Figure 17

Load capacities for different inclinations considering a torpedo anchor with zero, three, and four flukes and soil B: loads in plane 1

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Figure 18

Load capacities for different widths of the flukes considering a torpedo anchor with four flukes and soil B: loads in plane 1

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Figure 19

Load capacities for different angles between the plane of the loads and the flukes. Torpedo anchor with four flukes in soil B.

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Figure 14

Failure surfaces in soil B for different load inclinations, β, at the anchor: (a) 0 deg, (b) 15 deg, (c) 30 deg, (d) 45 deg, (e) 60 deg, (f) 75 deg, and (g) 90 deg

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Figure 13

Load versus normalized displacement curves of a torpedo anchor with four flukes embedded in soil C: loads in plane 1

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