Does modifying the particle size distribution of a granular material (i.e., material scalping) alters its shear strength?

Azéma, Émilien; Linero, Sandra; Estrada, Nicolás; Lizcano, Arcesio

doi:10.1051/epjconf/201714006001

Cited by 8 publications

(7 citation statements)

References 11 publications

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“…It is established that the strength properties of granular media result from the build-up of anisotropic structures of geometrical and mechanical origins (Rothenburg & Bathurst, 1989). The independence of strength with PSD in the case of mono-shaped particles has been discussed previously in the literature in Azema et al (2017), Azéma et al (2017), Estrada (2016), Voivret et al (2009), Nguyen et al (2015), and Cantor et al (2018). It has been attributed to a compensation mechanism which involves both the contact orientation anisotropy which decreases with the size span, and the branch length anisotropy which behaves inversely.…”

Section: Mechanical Behaviourmentioning

confidence: 87%

“…Numerical research 2D and 3D suggest that steady-state shear strength is independent of PSD for materials composed of unbreakable particles with similar shape across sizes (monoshaped) (Azema et al, 2017;Azéma et al, 2017;Estrada, 2016;Voivret et al, 2009;Nguyen et al, 2015;Cantor et al, 2018). This non-intuitive result motivated the investigation of particle size-shape correlation effects in greater detail in this research.…”

Section: Introductionmentioning

confidence: 84%

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Impact of grading on steady-state strength

Molina

Azéma

Estrada

et al. 2019

Géotechnique Letters

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In the mining industry, waste-dumps are earthen structures typically built by loose waste tipping. They may reach heights of hundreds of meters and undergo large deformations. For this reason, their stability design is based on the steady-state shear strength of the waste material. Waste materials are widely graded and may contain particles of up to metric order. Particle shape depends on the pattern of dissecting discontinuities at the source rock mass, and the relation between the size of the fragments and discontinuity spacing. The shear strength of this material is determined in the laboratory using scaled samples with altered Particle Size Distribution (PSD). However, altering the PSD is known to impact shear strength, and this impactis poorly studied. The representativeness of laboratory parameters obtained from scaled samples is thus arguable. Discrete element simulations are used here to investigate steady-state shear strength changes with alteration of the PSD when particle size and shape are correlated. It is observed, that shear strength changes result from the variation of the particle shapes induced by the alteration of the PSD. Consequently, identifying size-shape correlations and their potential impact on shear-strength is paramount when scaling materials for laboratory testing.

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Section: Mechanical Behaviourmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 84%

Impact of grading on steady-state strength

Molina

Azéma

Estrada

et al. 2019

Géotechnique Letters

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“…Numerical analysis to investigate the effect of only PSD alteration on shear strength, isolating the phenomenon from the influence of particle shape using the discrete element method (DEM), reveals that the steady state shear strength is invariant when altering the PSD in the specific case where the shape of the particles is kept constant across sizes and in the absence of crushing (Azéma et al 2017a(Azéma et al , 2017bEstrada 2016;Voivret et al 2009;Nguyen et al 2015;Cantor et al 2018).…”

Section: Introductionmentioning

confidence: 99%

“…This paper presents a summary of the main findings of a research project conducted to investigate when, why and how scaling of coarse granular materials affects its shear strength. Key outcomes of the project are separately published in Linero et al (2017Linero et al ( , 2019c and Azéma (2017aAzéma ( , 2017b, or under review for publication in Linero et al (2019aLinero et al ( , 2019b. This summary is drawn from each of these to provide specific advice to mine dump designers and operators, in a forum of geotechnical engineers who can appreciate the application of this work.…”

Section: Introductionmentioning

confidence: 99%

Influence of particle size-shape correlation on the shear strength of scaled samples of coarse mine waste

Linero¹,

Fityus²,

Simmons³

et al. 2020

Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering

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Coarse materials like rockfill and coarse mine waste must be scalped or scaled for shear strength testing in the laboratory as the size of commercial equipment is not big enough to test the full-scale material. Samples of coarse material prepared for testing differ from their prototypes in the characteristic sizes of the particles and/or the form of the particle size distribution (PSD) curve. The representativeness of the shear strength parameter determined in the laboratory on scaled samples is questionable, nevertheless they are typically used for geotechnical design without additional consideration. The particle shapes in a natural mine waste of colluvium sediments derived from eroded ancient sedimentary rocks from the Pilbara region of Australia was analysed and a correlation between shape and size was identified. The fragments have a particle shape ranging from slabs to sub-equant blocks with a tendency of larger particles to be flatter and platy. Therefore, material scaling for shear strength determinations inevitably alters not only the size of particles and proportion of sizes, but also the characteristic shapes of the material particles as it implies substituting larger (slabs) particles by smaller (sub-equant) particles. The direct-shear shear strength of a prototype sample of the colluvium sediment was evaluated in the laboratory, as well as two different scaled representations (models) with reduced maximum particle size. The scaled specimens, composed of more equant fragments due to the nature of the size-shape correlation, showed lower shear strength compared with the prototype sample. Simulations with a discrete element method reveal that the changes in the shear strength observed when altering the PSD are not due to the change in particle sizes. Instead, these changes in shear strength result from the variation of the particle shapes induced by the alteration of the PSD. This suggests that particle shape is a higher order factor than particle sizes and PSD shape on the shear strength of granular materials. This finding highlights the importance of particle shape quantification in soil classification and its consideration in activities such as sampling, sub-sampling, and scaling of coarse materials for geotechnical testing.

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“…Second, the effect of the PSD on the critical state is yet inconclusive based on the existing studies in literature. Some studies indicated that the critical state friction angle was related to PSD [17,18], while others [19,20] found that varying PSD had little influence on the critical state friction angle. Although it is widely accepted that PSD does have influence on the CSL location in e-p' plane [21][22][23][24][25][26], how the position of CSL in e-p' plane is influenced remains unclear.…”

Section: Introductionmentioning

confidence: 99%

The influence of particle-size distribution on critical state behavior of spherical and non-spherical particle assemblies

et al. 2018

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This paper presents an investigation into the effects of particle-size distribution on the critical state behavior of granular materials using Discrete Element Method (DEM) simulations on both spherical and non-spherical particle assemblies. A series of triaxial test DEM simulations examine the influence of particle-size distribution (PSD) and particle shape, which were independently assessed in the analyses presented. Samples were composed of particles with varying shapes characterized by overall regularity (OR) and different PSDs. The samples were subjected to the axial compression through different loading schemes: constant volume, constant mean effective stress, and constant lateral stress. All samples were sheared to large strains to ensure that a critical state was reached. Both the macroscopic and microscopic behaviors in these tests are discussed here within the framework of the anisotropic critical state theory (ACST). It is shown that both OR and PSD may affect the response of the granular assemblies in terms of the stress-strain relations, dilatancy, and critical state behaviors. For a given PSD, both the shear strength and fabric norm decrease with an increase in OR. The critical state angle of shearing resistance is highly dependent on particle shape. In terms of PSD, uniformly distributed assemblies mobilize higher shear strength and experience more dilative responses than specimens with a greater variation of particle sizes. The position of the critical state line in the e-p' space is also affected by PSD. However, the effects of PSD on critical strength and evolution of fabric are negligible. These findings highlight the importance of particle shape and PSD that should be included in the development of constitutive models for granular materials.

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Does modifying the particle size distribution of a granular material (i.e., material scalping) alters its shear strength?

Cited by 8 publications

References 11 publications

Impact of grading on steady-state strength

Impact of grading on steady-state strength

Influence of particle size-shape correlation on the shear strength of scaled samples of coarse mine waste

The influence of particle-size distribution on critical state behavior of spherical and non-spherical particle assemblies

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