Abstract
This paper presents new insights into the deformation response of sheared granular assemblies by characterising pore space properties from discrete element simulations of monodisperse particle assemblies in two-way cyclic shearing. Individual pores are characterized by a modified Delaunay tessellation, where tetrahedral Delaunay cells can be merged to form polyhedral cells. This leads to a natural partition of the pore space between individual pores with tetrahedral and polyhedral geometry. These are representative of small compact pores and larger well-connected pores, respectively. A scalar measure of pore orientation anisotropy during shearing is introduced. For triaxial shearing, larger pores align in the loading direction, while small pores are aligned perpendicular to the larger pores. Pore anisotropy mobilises at a slower rate than contact anisotropy or macroscopic stress state, and hence, is an important element to characterise in granular assemblies. Further, the distribution of pore volume remains isotropic. Pore shape was found to be a good micro-scale indicator of macroscopic density, with a strong relationship between averaged shape factor and macroscopic void ratio. Combining results for pore shape and orientation reveals an interesting interplay, where large elongated pores were aligned with the loading direction. These results highlight the importance of considering pore space characteristics in understanding the behaviour of granular materials.
Highlights
The macroscopic response of granular materials is influenced by microstructural characteristics of particles, their contacts and interstitial pores [22]
The current paper considers whether a partitioned subset of pores can be identified as the dominant contributors to pore space anisotropy
Note that the x-axis for two-way shearing has been unfolded into a single linear strain axis, and that a negative value of pore anisotropy is shown to allow for ease of comparison with the other parameters
Summary
The macroscopic response of granular materials is influenced by microstructural characteristics of particles, their contacts and interstitial pores (or voids) [22]. Interparticle contacts form a complex network and the associated anisotropy of this contact network provides insights into the nature of stress transmission and the development of shear strength [7,26,32]. The effect of pores (or more generally, pore space characteristics) on mechanical response of the medium has received relatively limited attention This may be attributed to the complexity associated with the description of continuous, entirely interconnected pore space in granular materials. Ghedia and O’Sullivan [6] extended this method to analyse digital images, while Muhunthan et al [21] and Muhunthan and Chameau [20] employed a similar technique in exploring the concept of yielding and an ultimate state boundary surface
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