MECHANISM OF CUT BLASTING

Blasting in a development heading or breasting operation starts from a cut, the purpose of which is to produce a void for the full depth of the planned round. The void provides a free face for the later-firing charges and is the most critical part of the round because the remaini ng holes cannot pull to the desired depth unless the cut flushes out a s planned. The burn cut is the most commonly used cut in Canadian unde rground mines. To elucidate the mechanism of cut blasting field experi ments were performed that involved drifting and separate cut blasts in a quarry face. Ground vibrations were monitored and some of the blast s were filmed with a high-speed camera. The results obtained during th e field tests are used as the basis for a description of the mechanism of breakage and flushing of rock in the cut. For effective flushing o f the broken rock the void provided by the relief holes should be appr oximately 15% of the cut volume. Guidelines for the proper design and sequencing of cut-holes are provided and problems encountered in cut-p ulling are discussed.