Controlled Fracture Techniques for Continuous Drill and Blast

摘要

The primary objective of the Phase I research effort was to evaluate the technical feasibility of using controlled fracture techniques to reduce the explosive loadings required in a small-charge continuous drill and blast machine. The program involved small-scale laboratory tests, conducted in both Plexiglas and granite, and large-scale tests, conducted in a hard-rock mine. Single-hole geometries, designed to induce fracturing from hole bottoms, and multiple-hole geometries, designed to pull rock from the face with longitudinally notched holes were studied. Excellent hole-bottom fracturing was consistently initiated in single unnotched but reasonably sharp holes with small explosive or propellant charges. Explosive charges caused excessive borehole fracturing and a consequent loss of borehole gas pressures. Conversely, propellant charges did not cause borehole damage and with the better gas retention were much more effective in achieving fracture propagation and efficient rock excavation. Results indicate that hole preparation techniques, charge loadings and hole stemming designs, based upon single-hole controlled fracture concepts, are applicable to an efficient continuous drill and blast system.