Different drilling and blasting strategies to improve blasting efficiency have been evaluated．The results of each strategy were compared by means of visual site investigation after blasting and calculating the total cost perton ofthe broken rock． Site investigation had shown that the third strategy had overcome the problem of unexploded ANFO．Unexploded ANFO was not seen after the blasting．and also visual inspection showed significant decrease in the number of oversize boulders．Another proper approach to evaluate different strategies is a comparison of unit production costs．
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Since the Objective is to minimize the production cost of per ton rock，then the resulting cost of each strategy should be calculated．For that reason，the comparable costs were estimated．Th ese are drilling cost，blasting cost and secondary breaking(hydraulic hammer)cost．
In this quarry，the required size of broken rock should be provided before loading for hauling．Th erefore a hydraulic hammer iS used to break oversize boulders.In order to estimate the drilling and secondary breaking cost of per ton limestone，the unit cost of driller and hydraulic ham er has been estimated as $／h that includes ownership and operating costs．The results were 54．1l$／h for driller and 44．46$／h for hydraulic ham er．Then the total working time of driller and ham er had been recorded for each blasting．Since the production of each blasting had been found by weighting，the unit production cost was calculated by multiplying the total working time with the unit cost of equipment and dividing the result by total pro—duction．The blasting cost consisted of the cost of ANFO．The summ ary of the resuits is...
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