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Estimation of soil strength in fine-grained soils by instrumented free-fall sphere tests

Estimation of soil strength in fine-grained soils by instrumented free-fall sphere tests
Estimation of soil strength in fine-grained soils by instrumented free-fall sphere tests

The dynamic response of a sphere in soft clay is considered through field tests in which a 0·25 m dia. steel sphere was allowed to free-fall in water and dynamically penetrate the underlying soft soil. The test data, collected in a lake and a sea environment, relate to sphere velocities of up to 8 m/s, reaching sphere invert embedments close to ten diameters. An inertial measurement unit located within the sphere measured the motion response of the sphere during free-fall and penetration in soil. The resulting acceleration data were used within a simple framework that accounts for both geotechnical shearing resistance and fluid mechanics drag resistance, but cast in terms of a single capacity factor that can be expressed in terms of the non-Newtonian Reynolds number. The merit of the framework is demonstrated by using it as a forward model in a series of inverse analyses that calculate the undrained shear strength profile from acceleration data measured in free-fall sphere tests. The good match between these profiles and those obtained from ‘push-in’ piezoball penetrometer tests points to the potential for an instrumented free-fall sphere to be used as a tool for characterising the near-surface strength of soft seabeds.

In situ testing, Penetrometers, Shear strength
0016-8505
959-968
Morton, J.P.
44775484-92cc-4aaf-b49d-f83f8c3be260
O’Loughlin, C.D.
d2821636-d20b-4fea-82fb-c1c64b53433c
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Morton, J.P.
44775484-92cc-4aaf-b49d-f83f8c3be260
O’Loughlin, C.D.
d2821636-d20b-4fea-82fb-c1c64b53433c
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93

Morton, J.P., O’Loughlin, C.D. and White, D.J. (2016) Estimation of soil strength in fine-grained soils by instrumented free-fall sphere tests. Geotechnique, 66 (12), 959-968. (doi:10.1680/jgeot.15.P.038).

Record type: Article

Abstract

The dynamic response of a sphere in soft clay is considered through field tests in which a 0·25 m dia. steel sphere was allowed to free-fall in water and dynamically penetrate the underlying soft soil. The test data, collected in a lake and a sea environment, relate to sphere velocities of up to 8 m/s, reaching sphere invert embedments close to ten diameters. An inertial measurement unit located within the sphere measured the motion response of the sphere during free-fall and penetration in soil. The resulting acceleration data were used within a simple framework that accounts for both geotechnical shearing resistance and fluid mechanics drag resistance, but cast in terms of a single capacity factor that can be expressed in terms of the non-Newtonian Reynolds number. The merit of the framework is demonstrated by using it as a forward model in a series of inverse analyses that calculate the undrained shear strength profile from acceleration data measured in free-fall sphere tests. The good match between these profiles and those obtained from ‘push-in’ piezoball penetrometer tests points to the potential for an instrumented free-fall sphere to be used as a tool for characterising the near-surface strength of soft seabeds.

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Morton et al 2016 AM - Accepted Manuscript
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More information

Accepted/In Press date: 25 May 2016
e-pub ahead of print date: 27 June 2016
Published date: 1 December 2016
Keywords: In situ testing, Penetrometers, Shear strength

Identifiers

Local EPrints ID: 419469
URI: http://eprints.soton.ac.uk/id/eprint/419469
ISSN: 0016-8505
PURE UUID: 2d1418f0-a479-430c-82e3-a3cda3574601
ORCID for D.J. White: ORCID iD orcid.org/0000-0002-2968-582X

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Date deposited: 12 Apr 2018 16:30
Last modified: 10 Jan 2022 03:11

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Contributors

Author: J.P. Morton
Author: C.D. O’Loughlin
Author: D.J. White ORCID iD

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