Micromechanical origin of angle of repose in granular materials

Dai, Bei‐Bing; Yang, Jun; Zhou, Cuiying

doi:10.1007/s10035-017-0709-6

Cited by 32 publications

(10 citation statements)

References 43 publications

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“…Aspherical grains and rough surfaces generally increase the resistance to such shearing 31 , and the tendency of aspherical grains to slide along the bed rather than roll further enhances frictional resistance. This argument is consistent with a compilation of bulk friction coefficients showing that less spherical granular materials generally have higher friction 2 , where A is the projected grain area and P is the projected perimeter (values closer to 1 indicate more spherical grains), for a compilation of observations [21][22][23] and the materials used in our experiments. d, Comparison of the still-water-settling drag coefficient, 𝐶 𝐷 settle , normalized by the drag coefficient for a sphere of the same volume (Methods) with a measure of grain shape -the Corey shape factor, 𝑆 𝑓 = 𝑐/√𝑎𝑏, where a, b, and c are the long, intermediate, and short axes of a grain, for a compilation of observations 24 and the materials used in our experiments.…”

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confidence: 91%

Grain shape effects in bed load sediment transport

Deal¹,

Venditti²,

Benavides³

et al. 2021

Preprint

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Bed load sediment transport, in which wind or water flowing over a bed of sediment causes grains to roll or hop along the bed, is a critically important mechanism in contexts ranging from river restoration to planetary exploration. Despite its widespread occurrence, predictions of bed load sediment flux are notoriously imprecise. Many studies have focused on grain size variability as a source of uncertainty, but few have investigated the role of grain shape, even though shape has long been suspected to influence transport rates. Here we show that grain shape can modify bed load transport rates by an amount comparable to the scatter in many sediment transport data sets. We develop a theory that accounts for grain shape effects on fluid drag and granular friction and predicts that the onset and efficiency of bed load transport depend on the mean drag coefficient and bulk friction coefficient of the transported grains. Laboratory flume experiments using a variety of grain shapes confirm these predictions. We propose a shape-independent sediment transport law that collapses our experimental measurements onto a single trend, allowing for more accurate predictions of sediment transport and helping reconcile theory developed for spherical particle transport with the behavior of natural sediment grains.

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supporting

confidence: 91%

Grain shape effects in bed load sediment transport

Deal¹,

Venditti²,

Benavides³

et al. 2021

Preprint

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“…The humble sandpile is probably the simplest and most common example of a collection of dry granular material; researchers have carried out a lot of works on the repose angle and the vertical stress distribution underneath the pile. Repose angle [5][6][7][8][9][10][11] is an important parameter to describe the microscopic and macroscopic mechanical properties of granular materials. Hamzah and Omar [7] have made a detailed review of the definition, measurement method, and application of the repose angle, and pointed out that the repose angle of the granular matter is usually quite different from the internal friction angle, and the above two angles are only close when the granular matter has uniform density, water content, particle size, and shape.…”

Section: Introductionmentioning

confidence: 99%

The experiment and analysis of the repose angle and the stress arch-caused stress dip of the sandpile

Fang

Guo

et al. 2021

Granular Matter

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The repose angle and characteristics of the vertical stress distribution beneath the sandpile can help to understand the physical and mechanical properties of the granular matter and guide the foundation design of the rock-soil deposits such as the rockfill dam and the storage structures of granular materials. Researches previously found that the stress dip phenomenon exists in piles constructed by the localized-source procedure, where the maximum vertical stress underneath the pile deviates from the center. The repose angle and the stress dip are affected by many internal and external factors and exhibit highly nonlinear and sensitive characteristics. However, the variation of the repose angle and the stress dip with influencing factors and the cause of the stress dip have not yet been fully explored. Based on the localized-source conical sandpile experiments and the discrete element method (DEM) simulation analysis, this paper studied the influences of the internal friction angle of granular matter and the construction history (the slowly raising funnel method SRFM and the fixed funnel method FFM) on the repose angle and the vertical stress dip beneath the pile; while the formation mechanism of the stress dip phenomenon was analyzed. The experimental results showed that the repose angle, physically different from the internal friction angle, has a relatively larger value and is positively related to the internal friction angle in the sandpile constructed by the FFM; the localized-source procedure and the internal friction angle are conducive to the formation of the macroscopic force chain arch structure in granular matter, which produces the arching effect and the stress shielding effect and leads to the stress dip beneath the pile; and the ratio of the stress dip RSD decreases with the increase of the local impact effect and the internal friction angle.

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“…One major limitation about the angle of repose in the current literatures is that particle size is usually limited to less than 10 millimetre [5,6,9,[11][12][13][14], and research on coarse particle assemblies with large sizes is still insufficient. Compared to soils or sands, coarse large-sized matters such as crushed rocks in dam engineering or ballast used as bearing materials in the railway system tend to have irregular morphologies, and the interlocking effects between particles are much more pronounced than that of small-sized substances, leading to different behaviors and properties in typical angle of repose tests.…”

Section: Introductionmentioning

confidence: 99%

“…However, research on the particle morphology effect on the angle of repose is limited. Generally, in the prevailing research, some simple-shape [6,9,11] or artificially created templates [12][13][14][18][19][20] are usually used in order to save computational time and to improve simulation efficiency.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Particle Morphology Effect on the Angle of Repose for Coarse Assemblies Using DEM

Chen

Gao

Liu

2019

Advances in Materials Science and Engineering

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The morphologies of coarse particles are usually irregular and play a dominant role in the mechanical behaviors of the particle assemblies. This paper quantitatively studies the effect of particle shape on the angle of repose, which is an important macroscopic parameter for ballast materials, via laboratory tests and numerical simulations by means of the discrete element method (DEM). Forty ballast particle templates and four simply created clump templates are reconstructed using an image-based method and quantified with two shape factors, sphericity and convexity. A series of simulations are conducted with the coefficient of sliding friction between particles changing from 0.2 to 0.6 at an interval of 0.1 to study its influence on various shapes of particles, and an appropriate value of sliding friction coefficient is chosen for the comparison of particle shape effect. The results show that increasing sphericity and convexity can significantly decrease the angle of repose, and the real ballast model gives a more realistic angle of repose behaviors as that of laboratory tests compared to simply created models. By analyzing the characteristics of particle motions and contacts from a microscopic perspective, the mechanism of particle shape attributed to the formation of granular aggregation is also discussed and revealed in this research.

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Micromechanical origin of angle of repose in granular materials

Cited by 32 publications

References 43 publications

Grain shape effects in bed load sediment transport

Grain shape effects in bed load sediment transport

The experiment and analysis of the repose angle and the stress arch-caused stress dip of the sandpile

Numerical Study of Particle Morphology Effect on the Angle of Repose for Coarse Assemblies Using DEM

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