Anisotropy of contact networks in granular media and its influence on mobilised internal friction

Sufian, Adnan; Russell, Adrian R.; Whittle, Andrew J.

doi:10.1680/jgeot.16.p.170

Cited by 18 publications

(28 citation statements)

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“…19. Restriction to the strong subset network was necessary as incremental fabric changes for the weak contact network were imperceptible (see Sufian et al [52] for a more general discussion of fractional networks). Figure 19 hence compares the change in vertical strain with the change in the vertical Probing from the isotropic state resulted in very small plastic deformations (Fig.…”

Section: From the Initial State O An Ordinary E-p-c Probe (O-b)mentioning

confidence: 99%

Micromechanical inspection of incremental behaviour of crushable soils

Ciantia

Arroyo²,

O’Sullivan

et al. 2019

Acta Geotech.

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In granular soils grain crushing reduces dilatancy and stress obliquity enhances crushability. These are well-supported specimen-scale experimental observations. In principle, those observations should reflect some peculiar micromechanism associated with crushing, but which is it? To answer that question the nature of crushing-induced particle-scale interactions is here investigated using an efficient DEM model of crushable soil. Microstructural measures such as the mechanical coordination number and fabric are examined while performing systematic stress probing on the triaxial plane. Numerical techniques such as parallel and the newly introduced sequential probing enable clear separation of the micromechanical mechanisms associated with crushing. Particle crushing is shown to reduce fabric anisotropy during incremental loading and to slow fabric change during continuous shearing. On the other hand, increased fabric anisotropy does take more particles closer to breakage. Shear-enhanced breakage appears then to be a natural consequence of shear-enhanced fabric anisotropy. The particle crushing model employed here makes crushing dependent only on particle and contact properties, without any pre-established influence of particle connectivity. That influence does not emerge, and it is shown how particle connectivity, per se, is not a good indicator of crushing likelihood.

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Section: From the Initial State O An Ordinary E-p-c Probe (O-b)mentioning

confidence: 99%

Micromechanical inspection of incremental behaviour of crushable soils

Ciantia

Arroyo²,

O’Sullivan

et al. 2019

Acta Geotech.

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“…Several axisymmetric loading paths considered in this study are: (a) constant volume triaxial compression (CV), which approximates the conventional undrained triaxial tests in laboratory; (b) constant radial stress triaxial compression (CR), which approximates the conventional drained triaxial tests; (c) constant mean stress triaxial compression (CP), which keeps the mean stress constant and compresses the specimen in the axial direction; (d) isotropic compression (ISOC), which compresses the specimen at identical rates in all three directions and (e) isotropic dilation (ISOD). During simulations, the strain ( ) and strain rate ( ̇ ) are estimated from the size and deformation of the periodic domain and the stress is estimated from the grains by the Love's equation as in the literature [17,25]:…”

Section: Discrete Element Modellingmentioning

confidence: 99%

“…The SFF equation relates the stress of granular material to some statistics of grain-scale entities which have clear physical meanings. The derivation of the SFF equation is extensively discussed in the literature [17,25]. Firstly, The summation in Eq.…”

Section: Normalised Contact Forcementioning

confidence: 99%

“…Figure 3c gives the normalised contact forces and it can be seen that contacts with larger f scatter around the whole specimen, but primarily oriented along z axis (the direction of major principal stress), which corresponds to the fact that grains of different groups have similar V (k) . It is extensively addressed in the literature that strong contacts are the dominant source in sustaining the deviatoric stress [25,29,30]. For the case in Fig.…”

Section: Normalised Contact Forcementioning

confidence: 99%

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A constitutive model for granular materials with evolving contact structure and contact forces—Part I: framework

He¹,

Wu²,

Wang³

2019

Granular Matter

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This and the companion paper present a constitutive model for granular materials with evolving contact structure and contact forces, where the contact structure and contact forces are characterised by some statistics of grain-scale entities such as contact normals and contact forces. And these statistics are actually the "fabric" or "force" terms in the "stress-force-fabric" (SFF) equation. The stress-strain response is obtained by inserting the predicted "fabric" or "force" terms from evolution equations into the SFF equation. Discrete element modelling is used to verify the slightly modified SFF equation and also to obtain the data of how the contact structure and contact forces evolve in various loading paths. It is demonstrated that a normalised contact force is a better measure of the contact forces in polydisperse granular assemblies and strong contacts should be contacts with larger normalised contact forces. The modified SFF equation is shown to predict the stress accurately. The constitutive equations regarding the response of the contact structure and contact forces are presented and they along with the SFF equation form a constitutive model, which is found capable of capturing the observed phenomena correctly and predicting the mechanical response in various loading conditions. The model is shown to be an extension to the hypoplastic models with more state variables.

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“…Micromechanics‐based numerical approaches represented by the discrete element method (DEM) are increasingly popular across many disciplines of engineering and science on capturing the mechanical behaviors of granular materials while providing grain‐scale insights . In geomechanics applications, DEM users commonly employ idealized spherical discrete elements to simulate granular grains due to the advantages this may offer, including easy contact detection and high computational efficiency . However, numerical studies have proven that grain shape underpins various facets of the mechanical responses for granular materials and should be properly accounted for in their modeling .…”

Section: Introductionmentioning

confidence: 99%

A poly‐superellipsoid‐based approach on particle morphology for DEM modeling of granular media

Zhao

2019

Num Anal Meth Geomechanics

112

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Summary Particle morphology plays a key role in affecting physical and mechanical behaviors of granular media. While various mathematical approaches and shape descriptors have been proposed to describe the morphological properties of granular particles, it remains a challenge to effectively incorporate them for efficient discrete modeling of granular materials. This study presents a new poly‐superellipsoid‐based approach for three‐dimensional discrete element method (DEM) modeling of non‐spherical convex particles. A uniform mathematical description of 3D poly‐superellipsoidal surface is employed to represent a realistic granular particle, which is shown to be versatile and effective in reproducing a wide range of shape features (including elongation, flatness, angularity, and asymmetry) for real particles in nature. A novel optimization approach based on hybrid Levenberg‐Marquardt (LM) and Gilbert‐Johnson‐Keerthi (GJK) algorithms is further developed for efficient and robust contact detection in DEM simulation of poly‐superellipsoidal assemblies. Simulations of granular packing and triaxial compression tests show that the proposed approach is generally robust and efficient for both dynamic and quasistatic modeling of granular media.

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Anisotropy of contact networks in granular media and its influence on mobilised internal friction

Cited by 18 publications

References 0 publications

Micromechanical inspection of incremental behaviour of crushable soils

Micromechanical inspection of incremental behaviour of crushable soils

A constitutive model for granular materials with evolving contact structure and contact forces—Part I: framework

A poly‐superellipsoid‐based approach on particle morphology for DEM modeling of granular media

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