Document Type : Research Paper



A comprehensive investigation was carried out to minimize the cost price of the rock fragmentation process including: drilling, blasting, secondary blasting and separating the large boulders (oversize rocks) while loading, until the optimized fragmentation, powder factor and ratio of burden (B) to blasthole diameter (?h) were achieved by doing several stages of drilling and blasting practically in different mines. The complicated in situ factors control rock fragmentation by blasting, as development of an adequate method for design of drilling and blasting had been a difficult task. Rock mass parameters affecting the powder factor and ratio were investigated extensively in different mines and discontinuity plane aperture of rock mass as a new parameter affecting the powder factor and ratio was also applied. Parameters affecting the rock mass fragmentation were summarized to be discontinuity plane aperture, discontinuity plane spacing, discontinuity plane orientation, rock mass description and unconfined compressive strength of rock material. The quantitative effect of each parameter on ratio was indicated by a number (rating). The total values of numbers were named “rock fragmentation index” (RFI). The numbers were arranged in a way that RFI was equal to ratio. Parameters of RFI and their rating were proposed in a table to use as a new simple method of blasthole pattern design.