Method and apparatus for controlled small-charge blasting of hard rock and concrete by explosive pressurization of the bottom of a drill hole

摘要

Rock and other hard materials, such as concrete, are fragmented by a controlled small-charge blasting process. A cartridge containing an explosive charge is inserted at the bottom of a hole drilled in the rock. The explosive charge is configured to provide the desired pressure in the hole bottom, including, if desired, a strong shock spike at the hole bottom to enhance microfracturing. The cartridge is held in place or stemmed by a massive stemming bar of high-strength material such as steel which blocks the flow of gas up the drill hole except for a small leak path between the stemming bar and the drill hole walls. The cartridge- incorporates additional internal volume designed to control the application of pressure in the bottom hole volume by the detonating explosive.