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The effect of permeability on the erosion threshold of fine-grained sediments

The effect of permeability on the erosion threshold of fine-grained sediments
The effect of permeability on the erosion threshold of fine-grained sediments

The erosion of marine sediments, although difficult to predict, can lead to important implications in offshore engineering, sedimentology and coastal management. Continued research is, therefore, warranted to compile high-quality erosion data from which to develop models to better predict the erosion resistance of different types of marine sediments. In this paper, dimensional analysis is performed to express the threshold shear stress as a function of a selection of soil properties that are commonly linked to the erosion process of sediments. To identify the dominant dimensionless group, an experimental investigation on the erosion threshold was carried out using fine-grained sediments that were systematically prepared to ensure variations in (i) particle size distribution (i.e. fines content), (ii) bulk density, and (iii) hydraulic permeability. The samples included silica, carbonate and marine sediments, each of which are expected to have limited or no clay-mineral content. The measurements were analysed and compared with existing literature and predictive models. It was found that marine sediment samples with limited fines content showed good agreement with the empirical Shields curve, irrespective of particle size distribution, bulk density and permeability. In contrast, for finer marine sediment it was found that variations in these soil properties modify the threshold shear stress away from the Shields curve. Across each of these parameters only permeability appeared to independently correlate with the observed range of threshold measurements. Motivated by this finding, a model is introduced to predict the threshold shear stress as a function of permeability and the reference erosion rate that is used to define when the threshold is reached. The resulting expression is shown to quantitatively explain the experimental data and is found to also agree with existing data from the literature for quartz sediments with a wide range in fines content. An apparent advantage of the new model is that it is consistent with existing studies that identify variations in threshold shear stress due to changes in bulk soil parameters – including fines content and bulk density – since each of these parameters also affect permeability.

Erosion threshold, Marine sediments, Model for predicting erosion threshold, Permeability, Sediment transport, Threshold shear stress
0378-3839
Mohr, Henning
2afb09e1-17c7-4875-ac8a-cd15850c1e91
Draper, Scott
efe46b7d-3989-403b-8b19-0b17dd54194f
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Cheng, Liang
3e5c1edf-17d3-4f54-9130-995bc16dd880
Mohr, Henning
2afb09e1-17c7-4875-ac8a-cd15850c1e91
Draper, Scott
efe46b7d-3989-403b-8b19-0b17dd54194f
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Cheng, Liang
3e5c1edf-17d3-4f54-9130-995bc16dd880

Mohr, Henning, Draper, Scott, White, David J. and Cheng, Liang (2021) The effect of permeability on the erosion threshold of fine-grained sediments. Coastal Engineering, 163, [103813]. (doi:10.1016/j.coastaleng.2020.103813).

Record type: Article

Abstract

The erosion of marine sediments, although difficult to predict, can lead to important implications in offshore engineering, sedimentology and coastal management. Continued research is, therefore, warranted to compile high-quality erosion data from which to develop models to better predict the erosion resistance of different types of marine sediments. In this paper, dimensional analysis is performed to express the threshold shear stress as a function of a selection of soil properties that are commonly linked to the erosion process of sediments. To identify the dominant dimensionless group, an experimental investigation on the erosion threshold was carried out using fine-grained sediments that were systematically prepared to ensure variations in (i) particle size distribution (i.e. fines content), (ii) bulk density, and (iii) hydraulic permeability. The samples included silica, carbonate and marine sediments, each of which are expected to have limited or no clay-mineral content. The measurements were analysed and compared with existing literature and predictive models. It was found that marine sediment samples with limited fines content showed good agreement with the empirical Shields curve, irrespective of particle size distribution, bulk density and permeability. In contrast, for finer marine sediment it was found that variations in these soil properties modify the threshold shear stress away from the Shields curve. Across each of these parameters only permeability appeared to independently correlate with the observed range of threshold measurements. Motivated by this finding, a model is introduced to predict the threshold shear stress as a function of permeability and the reference erosion rate that is used to define when the threshold is reached. The resulting expression is shown to quantitatively explain the experimental data and is found to also agree with existing data from the literature for quartz sediments with a wide range in fines content. An apparent advantage of the new model is that it is consistent with existing studies that identify variations in threshold shear stress due to changes in bulk soil parameters – including fines content and bulk density – since each of these parameters also affect permeability.

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The_effect_of_permeability_on_the_erosion_threshold_accepted - Accepted Manuscript
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Accepted/In Press date: 27 October 2020
e-pub ahead of print date: 4 November 2020
Published date: January 2021
Keywords: Erosion threshold, Marine sediments, Model for predicting erosion threshold, Permeability, Sediment transport, Threshold shear stress

Identifiers

Local EPrints ID: 445444
URI: http://eprints.soton.ac.uk/id/eprint/445444
ISSN: 0378-3839
PURE UUID: d166eee4-dc55-443f-8ae6-663a21cac798
ORCID for David J. White: ORCID iD orcid.org/0000-0002-2968-582X

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Date deposited: 09 Dec 2020 17:30
Last modified: 15 Sep 2021 02:14

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Contributors

Author: Henning Mohr
Author: Scott Draper
Author: David J. White ORCID iD
Author: Liang Cheng

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