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Penetrometer testing in a calcareous silt to explore changes in soil strength

Penetrometer testing in a calcareous silt to explore changes in soil strength
Penetrometer testing in a calcareous silt to explore changes in soil strength
This paper describes a centrifuge study using a range of penetrometer tests (T-bar, piezocone and free-fall piezocone) to explore changes in strength of reconstituted normally-consolidated natural calcareous silt. Various penetrometer test procedures were applied to measure the penetration resistance in this sample. The penetrometer test procedures included monotonic, cyclic and twitch-type movements as well as pauses for pore pressure dissipation. These mobilised combinations of partial or full remoulding, strain softening, consolidation and viscous rate effects. The penetrometer resistance – representing a proxy for strength – reduced by a factor of 4.1 from drained to undrained conditions (at the lowest fully undrained penetration rate). In undrained conditions, viscous enhancement of the penetration resistance raised the tip and shaft resistance in free fall piezocone tests by ∼2.8 and ∼3.6 times respectively. The ‘restart’ resistance immediately after the dissipation tests was ∼2.5 times higher than the resistance prior to dissipation, giving an indication of consolidation-induced strength gain. The ‘twitch’ test (using sequential steps decreasing the velocity) captured drainage and viscous rate effects, and also gave a ‘restart’ resistance that showed even greater consolidation effects than from a dissipation test. Overall, the different penetrometer test types and procedures measured resistances in the same soil sample that varied by a factor exceeding 20 from highest to lowest, resulting from different penetration rates and history, due to strain rate, strain level (or remoulding), and consolidation. An expression for the monotonic penetration resistance combining drainage and viscous rate effects was fitted to the response of all tests, spanning >7 orders of magnitude in strain rate.
Penetrometers, strain rate, drainage, offshore
0016-8505
Chow, Shiao Huey
7bbb0ede-4e74-46ad-8586-425fa5d2672a
O'Loughlin, Conleth D.
b0fc277d-6301-45fd-a2a5-438655f822b0
Zhou, Zefeng
2d62825a-660e-4052-a416-3ffde2dfeaa8
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Randolph, Mark
05c8dec9-cf94-42ef-8b4c-82bce017c82a
Chow, Shiao Huey
7bbb0ede-4e74-46ad-8586-425fa5d2672a
O'Loughlin, Conleth D.
b0fc277d-6301-45fd-a2a5-438655f822b0
Zhou, Zefeng
2d62825a-660e-4052-a416-3ffde2dfeaa8
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Randolph, Mark
05c8dec9-cf94-42ef-8b4c-82bce017c82a

Chow, Shiao Huey, O'Loughlin, Conleth D., Zhou, Zefeng, White, David J. and Randolph, Mark (2020) Penetrometer testing in a calcareous silt to explore changes in soil strength. Géotechnique. (doi:10.1680/jgeot.19.P.069).

Record type: Article

Abstract

This paper describes a centrifuge study using a range of penetrometer tests (T-bar, piezocone and free-fall piezocone) to explore changes in strength of reconstituted normally-consolidated natural calcareous silt. Various penetrometer test procedures were applied to measure the penetration resistance in this sample. The penetrometer test procedures included monotonic, cyclic and twitch-type movements as well as pauses for pore pressure dissipation. These mobilised combinations of partial or full remoulding, strain softening, consolidation and viscous rate effects. The penetrometer resistance – representing a proxy for strength – reduced by a factor of 4.1 from drained to undrained conditions (at the lowest fully undrained penetration rate). In undrained conditions, viscous enhancement of the penetration resistance raised the tip and shaft resistance in free fall piezocone tests by ∼2.8 and ∼3.6 times respectively. The ‘restart’ resistance immediately after the dissipation tests was ∼2.5 times higher than the resistance prior to dissipation, giving an indication of consolidation-induced strength gain. The ‘twitch’ test (using sequential steps decreasing the velocity) captured drainage and viscous rate effects, and also gave a ‘restart’ resistance that showed even greater consolidation effects than from a dissipation test. Overall, the different penetrometer test types and procedures measured resistances in the same soil sample that varied by a factor exceeding 20 from highest to lowest, resulting from different penetration rates and history, due to strain rate, strain level (or remoulding), and consolidation. An expression for the monotonic penetration resistance combining drainage and viscous rate effects was fitted to the response of all tests, spanning >7 orders of magnitude in strain rate.

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Chow et al 2019 AM 1 - Accepted Manuscript
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More information

Accepted/In Press date: 5 September 2019
e-pub ahead of print date: 10 September 2019
Published date: December 2020
Keywords: Penetrometers, strain rate, drainage, offshore

Identifiers

Local EPrints ID: 439478
URI: http://eprints.soton.ac.uk/id/eprint/439478
ISSN: 0016-8505
PURE UUID: 90ed1c00-e990-4d77-9f45-f48194dbdd8d
ORCID for David J. White: ORCID iD orcid.org/0000-0002-2968-582X

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Date deposited: 24 Apr 2020 16:30
Last modified: 28 Apr 2022 05:53

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Contributors

Author: Shiao Huey Chow
Author: Conleth D. O'Loughlin
Author: Zefeng Zhou
Author: David J. White ORCID iD
Author: Mark Randolph

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