31 Blast design considerations for underground mining and construction operations

Because the great majority of completely new fractures are created by tension, the dynamic tensile breaking strain (ε_t) is an important property of massive rocks. As the degree of natural fissuring increases, the influence of ε_t decreases whilst that of the pre-existing cracks becomes greater. Important and highly controllable blast parameters include the diameter and length of blastholes; the type and configuration of charges; the shape, condition and development of effective faces; the available expansion volume for broken rock; the type and dimensions of the blasthole pattern; and initiation sequence and delay timing. The effects of these several parameters on blast design, the results of blasting (and especially fragmentation and overbreak) and excavation costs are presented. Greatest consideration is given to tunnelling, sub-level open stoping and the excavation of caverns.

• NOTATION

• INTRODUCTION

• EFFECTS OF ROCK PROPERTIES

• EFFECTS OF DRILLING

• EFFECTS OF CHARGE PROPERTIES

• EFFECTS OF INITIATION AND PRIMING

• EFFECTS OF BLAST GEOMETRY

• EFFECTS OF INITIATION SEQUENCE AND DELAY TIMING

• CONCLUSIONS

• ACKNOWLEDGEMENT

• REFERENCE