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Strength of fine-grained soils at the solid-fluid transition

Strength of fine-grained soils at the solid-fluid transition
Strength of fine-grained soils at the solid-fluid transition

Deepwater offshore oil and gas developments require an assessment to be made of the risk of infrastructure damage from submarine slides. The likelihood and magnitude of submarine slides, and the consequent impact loading on seabed infrastructure in the path of the debris from the slide, must be estimated. Export pipelines are especially vulnerable to impact from submarine slides, because of their length and the need to cross canyons and other seabed features that are potential paths for the flowing debris. Characterising the debris material represents a particular challenge, as the original soil, which is typically characterised using conventional geotechnical methods, evolves through remoulding and water entrainment into a viscous fluid. Because of this transition from soil to fluid, characterisation of the strength of flowing fine-grained sediment has been addressed separately within a soil mechanics framework and a fluid mechanics framework, resulting in two different approaches for expressing the strain-rate-dependent strength of debris flows, and the consequential impact loads on pipelines. In this paper we compare the two approaches, and show that the geotechnical characterisation of fine-grained sediments can be extended into the liquid range in a continuous fashion. This is supported by a series of undrained shear strength measurements on two different remoulded soils, from fall cone tests, vane shear (including viscometer) tests, T-bar and ball penetrometer tests. Analysis of the results shows that the variation in shear strength over the solid and liquid ranges can be described by a unique function of water content, for a given soil. Furthermore, the effects of rate of shearing are well captured by a dimensionless function of the normalised strain rate. The geotechnical approach also accounts for the observed strength reduction due to intense shearing.

Clays, Constitutive relations, In situ testing, Landslides, Shear strength
0016-8505
213-226
Boukpeti, N.
3a09b546-4d1a-498d-986a-02165e5ab4fc
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Randolph, M.F.
75caa33a-e630-4ae8-84cd-758797bf9633
Low, H.E.
90be3458-b929-46d5-bebe-aebecb883989
Boukpeti, N.
3a09b546-4d1a-498d-986a-02165e5ab4fc
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Randolph, M.F.
75caa33a-e630-4ae8-84cd-758797bf9633
Low, H.E.
90be3458-b929-46d5-bebe-aebecb883989

Boukpeti, N., White, D.J., Randolph, M.F. and Low, H.E. (2012) Strength of fine-grained soils at the solid-fluid transition. Géotechnique, 62 (3), 213-226. (doi:10.1680/geot.9.P.069).

Record type: Article

Abstract

Deepwater offshore oil and gas developments require an assessment to be made of the risk of infrastructure damage from submarine slides. The likelihood and magnitude of submarine slides, and the consequent impact loading on seabed infrastructure in the path of the debris from the slide, must be estimated. Export pipelines are especially vulnerable to impact from submarine slides, because of their length and the need to cross canyons and other seabed features that are potential paths for the flowing debris. Characterising the debris material represents a particular challenge, as the original soil, which is typically characterised using conventional geotechnical methods, evolves through remoulding and water entrainment into a viscous fluid. Because of this transition from soil to fluid, characterisation of the strength of flowing fine-grained sediment has been addressed separately within a soil mechanics framework and a fluid mechanics framework, resulting in two different approaches for expressing the strain-rate-dependent strength of debris flows, and the consequential impact loads on pipelines. In this paper we compare the two approaches, and show that the geotechnical characterisation of fine-grained sediments can be extended into the liquid range in a continuous fashion. This is supported by a series of undrained shear strength measurements on two different remoulded soils, from fall cone tests, vane shear (including viscometer) tests, T-bar and ball penetrometer tests. Analysis of the results shows that the variation in shear strength over the solid and liquid ranges can be described by a unique function of water content, for a given soil. Furthermore, the effects of rate of shearing are well captured by a dimensionless function of the normalised strain rate. The geotechnical approach also accounts for the observed strength reduction due to intense shearing.

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More information

Published date: March 2012
Keywords: Clays, Constitutive relations, In situ testing, Landslides, Shear strength

Identifiers

Local EPrints ID: 419912
URI: https://eprints.soton.ac.uk/id/eprint/419912
ISSN: 0016-8505
PURE UUID: 823167ce-ff1f-4304-a9c6-a8bc9d6282af
ORCID for D.J. White: ORCID iD orcid.org/0000-0002-2968-582X

Catalogue record

Date deposited: 23 Apr 2018 16:30
Last modified: 14 Mar 2019 01:24

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Contributors

Author: N. Boukpeti
Author: D.J. White ORCID iD
Author: M.F. Randolph
Author: H.E. Low

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