The mechanics of precision presplitting

"Precision Presplitting is a widely used method of presplit blasting for the mining and construction industries. In recent years considerable effort has gone into the development of empirical equations based on field data to be able to better design the Precision Presplit for various rock types and structural environments. However, the most widely discussed theory about the mechanics of the presplit formation, that of shockwave collisions, does not appear to be applicable for this method of presplitting.This research has disproven this theory based on insufficient magnitude of the shockwave from modeling with basic wave mechanics. Other authors have suggested alternative theories based on the gas pressurization of the borehole. Recently the concept of hoop stresses as a result of the gas pressurization of the borehole was suggested. No method to analyze the gas pressurization of the borehole and magnitude of the hoop stresses existed. This research seeks to develop the basic theory to determine the hoop stress field for a Precision Presplit blast, using basic laws from thermodynamics and mechanics of materials to present a mathematical proof to determine the borehole pressure from a decoupled charge and the magnitude of the hoop stress developed in the rock.This modelling approach analyzes the stress from both the shockwave and gas pressure, which are quantified and compared to the tensile strength of the rock. This research shows that the shockwave magnitude is much too low to cause presplit formation while the hoop stress has sufficient magnitude to cause the split"--Abstract, page iii.