Discrete particle simulation of particulate systems: A review of major applications and findings

The size and shape of soil particles reflect the formation history of the grains. In turn, the macroscale behavior of the soil mass results from particle level interactions which are affected by particle shape. Sphericity, roundness, and smoothness characterize different scales associated with particle shape. New experimental data and results from published studies are gathered into two databases to explore the effects of particle shape on packing density and on the small-to-large strain mechanical properties of sandy soils. In agreement with previous studies, these data confirm that increased angularity or eccentricity produces an increase in emax and emin. Furthermore, the data show that increasing particle irregularity causes a decrease in stiffness yet heightened sensitivity to the state of stress; an increase in compressibility under zero-lateral strain loading; an increase in the critical state friction angle cs; and an increase in the intercept of the critical state line there is a weak effect on the slope . Therefore, particle shape emerges as a significant soil index property that needs to be properly characterized and documented, particularly in clean sands and gravels. The systematic assessment of particle shape will lead to a better understanding of sand behavior.

Particle Shape Effects on Packing Density, Stiffness, and Strength: Natural and Crushed Sands

▪ Abstract Field observations, laboratory experiments, and theoretical analyses indicate that landslides mobilize to form debris flows by three processes: (a) widespread Coulomb failure within a sloping soil, rock, or sediment mass, (b) partial or complete liquefaction of the mass by high pore-fluid pressures, and (c) conversion of landslide translational energy to internal vibrational energy (i.e. granular temperature). These processes can operate independently, but in many circumstances they appear to operate simultaneously and synergistically. Early work on debris-flow mobilization described a similar interplay of processes but relied on mechanical models in which debris behavior was assumed to be fixed and governed by a Bingham or Bagnold rheology. In contrast, this review emphasizes models in which debris behavior evolves in response to changing pore pressures and granular temperatures. One-dimensional infinite-slope models provide insight by quantifying how pore pressures and granular temperatures c...

Debris-flow mobilization from landslides

An experimental and numerical study of fracture coalescence in pre-cracked specimens under uniaxial compression

A review on the angle of repose of granular materials

Porosity influence on the shear strength of granular material–clay mixtures

Fractal analysis of the roughness and size distribution of granular materials

Ballast materials forming part of railway structures are subjected to cyclic loads. As a result of these loads, ballast densification, aggregate degradation, and lateral spread of the ballast material underneath the ties takes place inducing permanent deformations on the railways. Maintenance and rehabilitation costs of railtracks due to problems related with ballast performance are substantial, and millions of dollars are annually spent around the world in these activities. Understanding the crushable behavior of railtrack ballast could lead to the design of better railways that will reduce these costs. This paper presents the results of two discrete element method simulations intended to study the effect of crushing on the behavior of a simulated track ballast material forming part of a simulated track section. Even though the two simulations consider the same idealized material, crushing was allowed only in one simulation. The simulated track sections were subjected to a cyclic load, and the values of permanent deformation as a function of number of cycles were recorded. The obtained results showed that the induced permanent deformation strongly increased when considering particle crushing even though only a few particles were broken. Moreover, it was found that crushing concentrated underneath the simulated sleepers. Snap shots of the track sections are presented allowing a visualization of the evolution of crushing.

Discrete Element Method Analysis of Railtrack Ballast Degradation during Cyclic Loading

Many natural slopes and rockfill structures are made of a mixture of rock fragments and sand-size particles. To analyze the stability of such natural slopes and rockfills, a knowledge of how rocks...

Interpretation of the limits in shear strength in binary granular mixtures

Granular materials forming part of civil engineering structures are subjected to both static and dynamic loads. As a result of these loads, particle crushing occurs. This study focuses on the evolution of crushing in a simulated granular material subjected to a direct shear test. It was found that the discrete element method (DEM) can be used to visualize and understand the evolution of crushing experienced by a granular material during this test. Even though DEM does not normally consider particle breakage, it is possible to simulate crushing by replacing one particle that has failed in tension with a combination of many particles of different sizes. One simulation indicated that crushing did not develop uniformly throughout the sample, and the sample tended to achieve a fractal distribution of particle sizes. The changes in other properties of the simulated granular material such as porosity and shear strength were also recorded, analyzed, and compared to the changes produced during another simulation where crushing was not a predominant feature.

Luis E. Vallejo

Papers

Porosity influence on the shear strength of granular material–clay mixtures

Fractal analysis of the roughness and size distribution of granular materials

Discrete Element Method Analysis of Railtrack Ballast Degradation during Cyclic Loading

Interpretation of the limits in shear strength in binary granular mixtures

Discrete Element Method Evaluation of Granular Crushing Under Direct Shear Test Conditions