Fracture pattern of anisotropic rock by drilling or cutting using the PFC

Anisotropy plays a key role in fracture propagation models and rock fragmentation processes by rock drilling and cutting. Drilling tests with a percussive rock drill have been performed to examine the influence of anisotropy and inhomogeneity on fracture propagation in different rock types. Subsequently, thin sections of the bottom of the borehole were analyzed to get the associated crack patterns. Based on that, the attempt was made to simulate the drilling process in a specific rock material with the Particle Flow Code (PFC). Since the code is based on the discontinous mechanical approch, a rock sample is converted into an assembly of spheres, where the particles are able to interact with each other and fractures are able to propagate. Different rock cutting tools were applied such as button bits or disc cutters to penetrate different rock samples. The aim of the numerical simulation of the drilling and cutting processes was to examine the crack patterns in correlation with foliation. In this paper the first results of the PFC modeling are presented.