ABSTRACT
Recently, model experiments using PMMA specimens and electric detonators were carried out to observe the propagation of cracks between two charge holes in blasting by Nakamura et al. [12]. The applicability of the guide hole method using a circular hole having two notches between the charge holes was examined. Controlled blasting techniques produce the macrocrack in a desired direction and eliminate the generation of microcrack in the remaining rock. The principle behind these methods is that closely spaced parallel holes drilled on the final face are loaded with a light explosive charge that has a diameter smaller than that of the hole [13]. There are four methods of controlled blasting, and the one selected depends on the rock characteristic and the feasibility under the existing conditions. These methods are line drilling, cushion blasting, smooth-wall blasting and presplitting (also pre-shear) [14].
