Journal of the Korean Society of Mineral and Energy Resources Engineers ISSN:2288-0291(Print) 2288-2790(Online) 한국자원공학회지

This paper proposes the new methods which control the blast induced fractures more effectively than the conventional methods. The effectiveness of charge holder and notched hole that control blast induced fractures is proved through the experiments using cement mortar specimens and acryl plates and rated by controlled index. The notched hole and charge holder make it possible that the fractures propagate along the direction of the notches. However, these experiments show that the effect of charge holder is dependent on the material properties of charge holder and specimen, although the blast induced fractures accumulate at the direction of the notch. Therefore it is considered that notched hole is better method to control blast induced fractures than charge holder. The propagations of controlled fractures are affected by distance between notch and freeface. The more increases the ratio of notch directoin and minimum burden, the more decreases the effect of notched hole. Notched hole can control the blast induced fractures completely within the distance ratio of 1.5:1 between the notch direction and minimum burden.