The experiments reveal that the variation of rock strength is closely related to the microstructure of rocks. This study numerically investigates the microstructure of polycrystalline rock using a novel 3D Voronoi grain-based model. The particle growth method is first introduced to generate a dense sphere packing with prescribed gain size distribution. 3D Voronoi tessellation of the granular packing is then performed to obtain a polycrystalline rock sample. The distribution of the poly-crystals in varying shapes and sizes which represent different mineral grains is determined by petrographic data with 3D particle growth method. The numerical sample is in good agreement with the statistical characteristics of the microstructure of intact rocks. The uniaxial compression tests and tension tests are simulated by combined FDEM and cohesive crack propagation model. The results demonstrate that the numerical simulation agrees well with the experimental study. More importantly, the fracture patterns in the microscale are gained, similar to the results obtained on laboratory experiments. Therefore, this method can simulate the real microstructure of polycrystalline rocks, and provide valuable information in understanding the micro behavior of rock materials.Being the main component of the Earth's crust, rock is heavily involved in human engineering activity. Rock is a crude combination of different mineral grains, presenting difference in petrologic features, chemical composition and crystal structures. Petrologic features mainly include the mineral content, mineral grain size distribution and the degree of crystallization, which can be quantified through petrographic analysis by means of microscopic examination of the thin sections (Yilmaz
, 2011). Rocks are thus classified according to these characteristics. According to the degree of crystallization of the rock, the crystal structures can be divided into three categories: the eucrystalline texture, the hypocrystalline texture, and the glass structure. It can also be divided into three categories according to the mineral grain size in the rock: coarse grain, medium grain, and fine grain.
