Fremgangsmåte og apparat for styrt sprengning med liten ladning av hardt fjell og betong ved eksplosiv trykksetting av bunnen til et borehull

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.