Simulation of rock failure modes in thermal spallation drilling

Thermal spallation drilling is a contact-less means of borehole excavation that works by exposing a rock surface to a high-temperature jet flame. In this study, we investigate crucial factors for the success of such thermal drilling operations using numerical simulations of the thermomechanical processes leading to rock failure at the borehole surface. To that end, we integrate a model developed for spalling failure with our thermomechanical simulations. In particular, we consider the role of material heterogeneities, maximum jet-flame temperature and maximum jet-flame temperature rise time on the onset of inelastic deformation and subsequent damage. We further investigate differences in energy consumption for the studied system configurations. The simulations highlight the importance of material composition, as thermal spallation is favored in fine-grained material with strong material heterogeneity. The model is used to test the relationship between the jet-flame temperature and the onset of thermal spallation.