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

A novel discrete model for granular material incorporating rolling resistance

Computer simulations of crushable agglomerates were performed using the PFC3D computer code, which adopts the distinct element method (DEM). Agglomerates were made by bonding elementary spheres in ‘crystallo-graphic’ arrays, and by giving each sphere an existence probability of 0·8. Weibull statistics of the crushing strength of the resulting agglomerates, when tested singly between parallel platens, matches that of real silica sand grains. Triaxial tests on a cubical sample made of 389 agglomerates were then simulated. Curves of isotropic compression are shown, and the effect of loading rate on the position of the compression curves is discussed in relation to the practical question of performing DEM simulations as fast as possible without creating inertia errors. Other stress paths, including conventional ‘drained’ triaxial compression, constant mean effective stress, and constant-volume paths, were also simulated from different initial stresses along the virgin e–log p′ curve. The numerical results are...

http://www-civ.eng.cam.ac.uk/geotech_new/people/bolton/mdb_pub/129_Geotechnique_No53_Issue7_633_641.pdf

Discrete element simulation of crushable soil

The discrete element method has been used to model railway ballast Particles have been modelled using both spheres and clumps of spheres A simple procedure has been developed to generate clumps which resemble real ballast particles much more so than spheres The influence of clump shape on the heterogeneous stresses within an aggregate has been investigated, and it has been found that more angular clumps lead to a greater degree of homogeneity A box test consisting of one cycle of sleeper load after compaction has been performed on an aggregate of spheres and also on an alternative aggregate of clumps The interlocking provided by the clumps provides a much more realistic load- deformation response than the spheres and the clumps will be the basis for future work on ballast degradation under cyclic loading

The importance of modelling ballast particle shape in the discrete element method

Soil–geosynthetic interaction: Modelling and analysis ☆

A discrete element model has been developed for geogrid-reinforced ballast. A model for unreinforced ballast has first been developed and evaluated using simulations of large-scale triaxial experiments and comparing with available data. A model for the geogrid has also been developed by bonding many small balls together to form the desired geometry and evaluated by simulating standard tests. The discrete element method (DEM) has then been used to model the interaction between ballast and geogrid by simulating pull-out tests and comparing with experimental data. The DEM simulations have been shown to predict well the peak mobilised resistance and the displacement necessary to mobilise peak pull-out force. The effect of the ratio of the geogrid aperture size to ballast particle diameter on pull-out resistance has also been investigated. The zone of influence of the geogrid has also been examined by simulating larger-scale pull-out tests in addition to cyclic triaxial tests. The method holds much promise as ...

Discrete element modelling of geogrid-reinforced aggregates

Discrete element modelling of soil particle fracture

Discrete element modelling of yielding and normal compression of sand

This paper examines the discrete element modelling of cyclic loading of an aggregate of crushable sand grains. Each grain of sand is modelled as an agglomerate of balls bonded together. The aggregate is subjected to compaction followed by isotropic normal (plastic) compression, and then unloaded to half the maximum applied stress. The aggregate is then subjected to cyclic loading to a maximum stress ratio of 0.8. The aim of the paper is to examine the reduction of the rate of axial strain with number of cycles, and to determine the relative influences of volumetric strain and shear strain rates on the axial strain rate. In particular, the paper aims to show whether particle breakage is mainly related to the accumulation of volumetric strain. This is found to be the case, which is consistent with proposals by other authors that plastic hardening under monotonic loading is due to particle fracture.

Discrete element modelling of cyclic loading of crushable aggreates

coupled constitutive equations for a saturated porous medium are developed in the frame of the theories of mixtures : the fluid constituent is elastic and the solid skeleton behaves as a rate-independent elastic-plastic solid. Then the existence of real acceleration wave-speeds is considered : actually the analysis centers on the modes in which these wave-speeds cease to be real. An explicit criterion indicating the critical value of the plastic modulus at the onset of a stationary discontinuity (one wave-speed is zero) is derived in both cases where the fluid and solid constituents are compressible and where they are not. Furthermore, it is shown that in some circumstances, some wave-speeds cease to be real in the very early stages of the inelastic deformation process due to the incipience of a flutter instability (two wave-speeds are complex conjugate). When it is not excluded, this mode of loss of hyperbolicity of the dynamic equilibrium equations usually precedes the onset of a stationary discontinuity and may occur right at the inception of plastic loading, that is for an infinitely large plastic modulus. Flutter instability is excluded when the plastic behavior of the solid skeleton is associative and its existence depends strongly on the relative positions of the shear and longitudinal elastic wave-speeds. It is not likely to occur if the shear wave-speed is the smallest elastic wave-speed and then a stationary discontinuity prevails.

Ouahid Harireche

Papers

Discrete element modelling of geogrid-reinforced aggregates

Discrete element modelling of soil particle fracture

Discrete element modelling of yielding and normal compression of sand

Discrete element modelling of cyclic loading of crushable aggreates

Acceleration waves, flutter instabilities and stationary discontinuities in inelastic porous media