The size distribution of fragmented rocks depends on not only the blasting standard but also the mechanical properties, joint system and crack density of rock mass. As, especially, the cracks in the rock mass are heavily developed at the limestone quarries in Japan, the joints and/or cracks in the rock mass have big impacts on the blasting effects such as the size of fragmented rocks. Therefore, if the joint system and/or crack density in the rock mass can be known and evaluated in quantity, the blasting operation can be done more effectively, efficiency and safety. However, the guideline for designing the appropriate blasting standard based on the rock mass condition such as mechanical properties, joint system and/or distribution of cracks, discontinuities, from the scientific point of view, has not been developed yet. Therefore, a series of blasting tests had been conducted in different mines and faces, geological conditions and blasting standards in order to know the impacts of each factor on the blasting effects. This paper summarizes the results of blasting tests and describes the impacts of rock mass conditions and blasting standard on the size of fragmented rocks.
Rock fragmentation is one of the major concern in surface mining because of its strong influence on the efficiency and productivity of the mining operation. Although past researches show that the size of rock fragmentation can be controlled by optimizing blasting designs, the effects of blasting designs or prediction methods of the size of rock fragmentation have not yet been discussed enough yet. In addition, the research works only focused on the controll and prediction of means size of the rock fragmentation. However, they have not considered the uniformity of the rock fragmentation despite all the size of rock fragmentation sould be ideally same in terms of efficiency. Firing patttern including delay time is one of the blasting designs which can be easiliy altered and has low impact on the production. Therefore, the effect of firing pattern on both the size and uniformity of rock fragmentation was discussed in this study. The results showed that two directions of firing pattern had advantage in terms of both mean size and uniformity of rock fragmentation.
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