Fracture Propagation in Anisotropic Rock During Drilling and Cutting

Anisotropy plays a key role in fracture propagation models and rock fragmentation processes during 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 analysed to investigate the associated crack patterns. Based on these observations an attempt was made to simulate the drilling process in a specific rock material using the Particle Flow Code (PFC2D). Since the Particle Flow Code is based on a discontinuum mechanics approach, the 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 assumed including button bits, disc cutters and roadheader bits to simulate the penetration of varying rock samples. The latter have been omitted in this paper due to space limitations. The aim of the numerical simulation of the drilling and cutting processes was to examine the crack patterns and correlate with existing foliation. In this paper preliminary results of the 2-dimensional PFC modelling are presented.