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Analysis of soil strength degradation during episodes of cyclic loading, illustrated by the T-Bar penetration test

Analysis of soil strength degradation during episodes of cyclic loading, illustrated by the T-Bar penetration test
Analysis of soil strength degradation during episodes of cyclic loading, illustrated by the T-Bar penetration test

Pipelines and risers form an essential part of the infrastructure associated with offshore oil and gas facilities. During installation and operation, these structures are subjected to repetitive motions which can cause the surrounding seabed soil to be remolded and soften. This disturbance leads to significant changes in the operative shear strength, which must be assessed in design. This paper presents an analytical framework that aims to quantify the degradation in undrained shear strength as a result of gross disturbance-in this case through repeated vertical movement of a cylindrical object embedded in undrained soil. The parameters of the framework were calibrated using data obtained in a geotechnical centrifuge test. In this test a T-bar penetrometer, which is a cylindrical tool used to characterize the strength of soft soil, was cycled vertically in soil with strength characteristics typical of a deep water seabed. Using simple assumptions regarding the spatial distribution of "damage" resulting from movement of the cylinder, and by linking this damage to the changing undrained shear strength via a simple degradation model, the framework is shown to simulate well the behavior observed in a cyclic T-bar test. This framework can potentially be extended to the similar near-surface behavior associated with seabed pipelines and risers.

Clays, Offshore pipelines, Shear strength, Soil-pipe interaction, Strain softening
1532-3641
117-123
Hodder, M.S.
2c7413ea-6ff3-42ec-b93c-8ac67cede77e
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Cassidy, M.J.
095b5237-97db-4ee5-9cb1-0b68d4731497
Hodder, M.S.
2c7413ea-6ff3-42ec-b93c-8ac67cede77e
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Cassidy, M.J.
095b5237-97db-4ee5-9cb1-0b68d4731497

Hodder, M.S., White, D.J. and Cassidy, M.J. (2010) Analysis of soil strength degradation during episodes of cyclic loading, illustrated by the T-Bar penetration test. International Journal of Geomechanics, ASCE, 10 (3), 117-123, [004003QGM]. (doi:10.1061/(ASCE)GM.1943-5622.0000041).

Record type: Article

Abstract

Pipelines and risers form an essential part of the infrastructure associated with offshore oil and gas facilities. During installation and operation, these structures are subjected to repetitive motions which can cause the surrounding seabed soil to be remolded and soften. This disturbance leads to significant changes in the operative shear strength, which must be assessed in design. This paper presents an analytical framework that aims to quantify the degradation in undrained shear strength as a result of gross disturbance-in this case through repeated vertical movement of a cylindrical object embedded in undrained soil. The parameters of the framework were calibrated using data obtained in a geotechnical centrifuge test. In this test a T-bar penetrometer, which is a cylindrical tool used to characterize the strength of soft soil, was cycled vertically in soil with strength characteristics typical of a deep water seabed. Using simple assumptions regarding the spatial distribution of "damage" resulting from movement of the cylinder, and by linking this damage to the changing undrained shear strength via a simple degradation model, the framework is shown to simulate well the behavior observed in a cyclic T-bar test. This framework can potentially be extended to the similar near-surface behavior associated with seabed pipelines and risers.

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More information

Accepted/In Press date: 9 September 2009
e-pub ahead of print date: 30 September 2009
Published date: May 2010
Keywords: Clays, Offshore pipelines, Shear strength, Soil-pipe interaction, Strain softening

Identifiers

Local EPrints ID: 419881
URI: http://eprints.soton.ac.uk/id/eprint/419881
ISSN: 1532-3641
PURE UUID: dd445f66-237c-4384-b79b-d22575c62919
ORCID for D.J. White: ORCID iD orcid.org/0000-0002-2968-582X

Catalogue record

Date deposited: 23 Apr 2018 16:30
Last modified: 15 Oct 2019 00:25

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