NUMERICAL-SIMULATION AND FIELD TESTING OF FLAME-JET THERMAL SPALLATION DRILLING .1. MODEL DEVELOPMENT

Certain polycrystalline rocks will fracture into thin, disk-like fragments when exposed to rapid surface heating. Some current hard-rock drilling methods using supersonic flame-jets as heat sources exploit this behavior for efficient granite quarrying or blasthole formation. Recent extensions of Weibull's theory of rock failure to quantitatively analyze rock spallation are employed to estimate spall size distributions and rock surface temperatures at the onset of spallation. A numerical drilling simulation code incorporating rock failure criteria and turbulent flow effects is developed to predict spallation rates and hole radii under field-drilling conditions. Because an accurate description of heat transfer through a turbulent wall jet is required, the wall-function method is generalized in a crude way to account for compressible flow past roughened, non-adiabatic rock surfaces.