The paper presents a study of particle shape effect on microstructure within granular materials in gravitational environments using samples acquired from three-dimensional (3D) discrete element method (DEM) modeling and simulation (M&S) of gravitational pluviations. Three-axis ellipsoidal particles with various aspect ratios are examined for their spatial orientations, and the three-axis probability density functions (PDF) are analyzed, before and after pluviation. A complicated data structure, convex hull, is employed to construct tetrahedra that connect particle centroids, and investigate theinternal topology and fabric of particle assemblies composed of various particle shapes. The Qhull-constructed connected tetrahedra within granular materials may serve as a useful tool to study the geometrical fabric (such as tetrahedron shape, solid angles, void ratio, etc), investigate particle collision requirements in sample preparation, describe strain/deformation/failure mechanisms, and explore stress distribution over granular materials.