The Effect of Drilling and Charging Design on Cost of Blasting in Some Selected Rocks in Nigeria

Saliu M. A., Ajaka E.O., Ohere S. A.

This research investigates the effects of drilling and charging specifications on blasting cost in three selected rocks; granite, limestone and marble in Nigeria. In order to achieve this, the three rock types were characterized to determine some rock properties; uniaxial compressive strength, point load strength, Schmidt hardness and unit weight. Drilling and charging design parameters; burden, spacing, blasthole diameter, blasthole depth, stemming height, and specific charge were obtained by blast design variations using Langerford model. The cost of blasting was estimated from all input parameters; cost of explosives and explosives accessories, drill tools and accessories, and costs of other related items and activities. Sensitivity analysis was performed by selecting combination of controllable and uncontrollable (design and rock) factors over a range of value to determine the variation of cost with drilling and charging specifications for each of the selected rock types. The results obtained show that hole diameter increase with corresponding increase in blasting cost and no significant change in the drilling cost for all the three rock types. Also, increase in bench height brings about a corresponding increase in both drilling and blasting cost. Increase in burden or spacing decreases the number of holes to be drilled and consequently the amount of explosives needed for the blast. The optimum cost for granite, marble and limestone are; ₦15,000,000, ₦10,000,000 and ₦8,000,000 respectively.  It can then be observed that the optimum drilling and blasting cost is dependent on the strength properties of a rock to be blasted and that the higher the strength of the rock, the higher the optimum cost required to achieve desired fragmentation. The research shows that optimum cost analysis is an important parameter required to find a common ground between optimum costs and desired fragmentation.