Further Evaluation of a Ligamented Split-Tube for Fracture Control in Blasting.

摘要

This report describes laboratory tests conducted to investigate the effectiveness of a ligamented split-tube charge holder in producing controlled fracture planes in thick plexiglas and rock models. The ligamented split-tube produces stress concentrations at the tube slits and initiates the cracks at preselected locations. The tube serves to protect the remaining portion of the borehole and to eliminate parasitic cracking. Since the number of cracks initiated is small,the residual gas pressure from a highly cushioned charge is sufficient to drive the cracks along the radially oriented fracture control planes for long distances. The results of the test program were positive in both plexiglas and granite models. A very high degree of fracture control was achieved when the ligaments on the split tube were properly sized and when the charge was carefully cushioned.