This research investigate the causes of quarry elevated floors, poor fragmentation, and formation of toes in the Jolex Construction Company Quarry and recommends best practices in order to provide good working pit floors and to eliminate or reduce the cost of secondary breakage. The methods employed includes: drilling performance analysis using statistical tools, modification of secondary breakage cost estimation model using two different existing models, and estimation of the cost of secondary drilling and blasting using the designed modification model and other two existing models; sensitivity analysis. From the analysis, it was observed that the blast designed parameters and blasting practices (desk design) were acceptable to produce good fragmentation and good working pit and bench floors but the actual drilling parameters deviated from the designed parameters by about 26%, 19%, 26% and 2% in hole depth, burden, spacing and hole inclination respectively. It was concluded that the cause of the ineffective fragmentation leading to high cost of secondary breakage and uneven pit floors was due to operational errors during drilling. It is recommended that combine field experience and theoretical knowledge of drill and blast geometry be used during drilling activities for accuracy and precision of all blast holes.

Keywords: fragmentation, sensitivity analysis, drilling, blasting