Evolution of pore characteristics in the 3D numerical direct shear test

The quantitative analysis of the pore characteristics of granular materials has been often challenging due to arbitrarily shaped geometry of pores despite its significant implications. In this study, we investigate the size distribution and orientation of pores in dilative and contractive assemblies in the direct shear test by performing 3D discrete element simulations in conjunction with image processing of pore geometry. We quantitatively define unit pores by the Delaunay Tessellation followed by pore mergence and fitting them with ellipsoids. It is observed that the evolution of pore size distribution depends on the dilatancy of assemblies. Results also show that the direction of principal stresses governs the orientations of pores during shearing, with respect to the size of pores. This study highlights that the dominant factors of the pore characteristics upon shearing are stress anisotropy and particle mobilization to make the internal structure stable.