@proceedings {365, title = {AIP Conference Proceedings A multiscale description of failure in granular materials}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {585-588}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

This paper presents conditions of initiation and development of failure in granular materials through a twodimensional discrete element model. General condition for the effective development of failure and its physical characteristics are recalled. Then relation between failure and the second order work expressed in terms of microscopic variables is discussed. Eventually, correspondence between a localized mode of failure marked with shear band patterns and space distribution of negative values of microscopic second-order work is investigated.

}, doi = {10.1063/1.4811999}, author = {Hadda, Nejib and Fran{\c c}ois Nicot and Sibille, Luc and Farhang Radja{\"\i} and Tordesillas, Antoinette and Darve, F{\'e}lix}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {366, title = {AIP Conference ProceedingsTumbling sandpiles in a fluid}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-2013}, pages = {662-665}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

By means of contact dynamics simulations interfaced with computational fluid dynamics, we analyze the effect of a suspending fluid on the dynamics of collapse and spread of a granular column. We find that the runout distance increases as a power law with the aspect ratio of the column and, for a given aspect ratio, it may be the same in the grain-inertial and fluid-inertial regimes but with considerably longer duration in the latter case. We show that, in both viscous and fluid-inertial regimes, this behavior results from compensation between two effects of the fluid: 1) reduction of the kinetic energy during collapse and 2) enhancement of the flow by lubrication during spread.

}, doi = {10.1063/1.4812018}, author = {Farhang Radja{\"\i} and Vincent Topin and Perales, F. and Yann Monerie}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {367, title = {A benchmark for particle shape dependence}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {883-886}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Particle shape is a major parameter for the space-filling and strength properties of granular materials. For a systematic investigation of shape effect, a numerical benchmark test was set up within a collaborative group using different numerical methods and particles of various shape characteristics such as elongation, angularity and nonconvexity. Extensive 2D shear simulations were performed in this framework and the shear strength and packing fraction were compared for different shapes. We show that the results may be analyzed in terms of a low-order shape parameter \η describing the degree of distortion from a perfectly circular shape. In particular, the shear strength is an increasing function of \η with nearly the same trend for all shapes, the differences being of second order compared to \η. We also observe a nontrivial behavior of packing fraction which, for all our simulated shapes, increases with \η from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as \η is further increased. Finally, the analysis of contact forces for the same value of \η leads to very similar statistics regardless of our specific particle shapes.

}, doi = {10.1063/1.4812073}, author = {Gael Combe and C{\'e}cile Nouguier-Lehon and Emilien Az{\'e}ma and Krzysztof Szarf and Baptiste Saint-Cyr and Marie Chaze and Farhang Radja{\"\i} and Pascal Villard and Jean-Yves Delenne and Vincent Richefeu and Philippe Sornay and Charles Voivret and CEGEO Group}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {369, title = {Capillary states of granular materials in the funicular state}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {1023-1026}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Using a multi-phase lattice Boltzmann model, we investigate the capillary states of a 2D granular packing gradually saturated by condensation from a homogeneously injected vapor phase. The internal stresses induced by surface tension and Laplace pressure are directly calculated from the forces acting on the grains with increasing amount of liquid. The evolution of cohesive strength with the amount of liquid reveals four different states reflecting the connectivity of the liquid phase and local grain environments. It increases in the pendular state, characterized by binary liquid bridges holding the grains together, and within the funicular state with an increasing number of liquid clusters connected to several grains. Beyond 40\% of saturation, the cohesive strength falls off due to a decreasing Laplace pressure of liquid clusters.

}, doi = {10.1063/1.4812108}, author = {Jean-Yves Delenne and Vincent Richefeu and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {368, title = {Comparison of the effects of rolling resistance and angularity in sheared granular media}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-2013}, pages = {891-894}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. For this purpose, we use contact dynamics simulations. By means of a simple shear numerical device, we investigate the mechanical behavior of these materials in the steady state in terms of shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. We find that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.

}, keywords = {angularity, anisotropy, force distribution, Granular material, rolling resistance, Shear strength, solid fraction}, url = {https://hal.archives-ouvertes.fr/hal-00842799}, author = {Estrada, Nicolas and Emilien Az{\'e}ma and Farhang Radja{\"\i} and Taboada, Alfredo}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {360, title = {Penetration strength of coarse granular materials from DEM simulations}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 }, year = {2013}, month = {Jun-18-2013}, pages = { 241-244}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer test is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. In fact, the data are considerably more sensitive to various parameters such as fabric structure, particles shape or the applied impact energy. In order to achieve a better understanding of the underlying phenomena, we performed a numerical study by means contact dynamics DEM simulations. We consider the penetration of a moving tip into a sample composed of irregular grain shapes and we analyze the influence of the driving velocity and applied energy on the penetration strength. We find that the latter grows with both the penetration rate and energy. Force fluctuations on the tip involve a jamming-unjamming process. The typology of contact network and inter-granular friction play a major role in the fluctuations and measured values of the cone penetration strength.

}, doi = {10.1063/1.4811912}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {361, title = {Settlement statistics of a granular layer composed of polyhedral particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {333-336}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

We use 3D contact dynamics simulations to investigate the mechanical equilibrium and settlement of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction force at the top and bottom boundaries, the transient deformation induced by a constant vertical load increment is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation.

}, doi = {10.1063/1.4811935}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {363, title = {Shear strength and microstructure of 3D assemblies of platy particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-09-2013}, pages = {519-522}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

As a first step towards particle-scale modeling of clayey soils, we investigate the mechanical behavior and microstructure of assemblies of three-dimensional rectangular platy particles by means of the discrete element method. Several samples composed of particles of different levels of platyness (ratio of width to thickness) were numerically prepared and sheared to large deformations. We analyze the shear strength, packing fraction, connectivity, contact and force anisotropies, and mobilization of friction forces as functions of platyness.We find that both the mechanical behavior and microstructure are strongly dependent on the degree of platyness. This happens, in particular, because of the alignment of particle faces along a particular direction. Additionally, as observed for other granular materials with complex shapes, the packing fraction passes by a peak value before decreasing for larger values of platyness.

}, keywords = {Clays, DEM, Microstructure, Shear strength}, url = {https://hal.archives-ouvertes.fr/hal-00842787}, author = {Boton, Mauricio and Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i} and Lizcano, Arcesio}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {362, title = {Shear strength, force distributions and friction mobilization in sheared packings composed of angular particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {2013}, pages = {511-514}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we explore the effect of particle shape angularity on the mechanical behavior of sheared granular packings. A first series of contact dynamics simulations is performed in 2D with regular polygons with an increasing number of sides ranging from 3 (triangles) to 60. Then, in order to approach \“idealized\” angular particles, a second series of simulations is performed in 3D with irregular polyhedra with the number of faces ranging from 8 (octahedron-like) to 596. A counterintuitive finding is that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below 6 sides in 2D and 46 faces in 3D). A micromechanical analysis of force and contact orientations, all enhanced by face-face and face-side contacts, reveals that this increase is due to an increase of both contact and force anisotropies, and the saturation for higher angularities is a consequence of a rapid fall-off of the contact and normal force anisotropies compensated by an increase of the tangential force anisotropy.

}, doi = {10.1063/1.4811980}, author = {Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} }