A statistical bonded particle model study on laboratory scale rock drilling

Rock drilling is a crucial process in many industries, one example being the mining industry, where it is used for exploration and blasting. In a typical rock drilling process, the rock surface is fractured by dynamic mechanical interaction with a drill bit, resulting in rock fragments detaching from the surface. These cuttings are then transported through the borehole via water or air, and the rock fragment size is important for efficient borehole flushing. In this work, a heterogeneous bonded particle model was calibrated and applied to a laboratory scale rock drilling process. The mineral grain structure was obtained from an electron microscope scan of the rock surface, and the average grain size, volume percentage and stiffness of the three most common minerals were represented in the model. The dynamic mechanical behaviour of the rock material was obtained by conducting uniaxial compression and Brazilian disc tests in a split-Hopkinson pressure bar configuration. The results were used to calibrate the model. After the heterogeneous model was shown to be able to capture the macroscopic strengths and fracture modes of the split-Hopkinson experiments, it was used to simulate the laboratory scale rock drilling experiment, where two tool indentation depths were investigated. Here, the simulation was compared to experimental results in terms of vertical load acting on the tool, machine compliance as well as rock-cutting size distributions. The results from the simulation were in good agreement with the experimental observations.