Influence of mechanical and aggregate properties of rock on powder factor in rock blasting

Abstract

Quarry metal is a widely used material in any large scale construction industry. Though demand for quarry metal substantially increased due to recently emerged large infrastructure development projects in Sri Lanka such as highway and port city, profit margins of the quarrying has drastically reduced due to high powder factors recorded in recent rock blasting activities of local quarries. Most possible reason for realizing high powder factors could be the introduction of various new explosive agents such as water-gel in to the local mining industry. Importance of analysing the influence of mechanical and aggregate rock properties on powder factor arises in this context to allow seeking suitable rocks those incur minimum blasting expenditure during the production stage. Outcomes of the project can be used to predict powder factor which could be achieved in blasting operations of a certain rock even before starting the quarry operations to minimize its production cost in the long run. Eight quarries operates under the close supervision of qualified Mining Engineers were selected for this study to ensure blasting geometry and configurations have being properly managed during the realized powder factor data recorded time period. Random core samples were obtained from each quarry site and they were tested for Density, Uniaxial Compressive Strength (UCS) and Tensile Strength. Similarly, random aggregate samples were taken and performed the Aggregate Impact Value (AIV) test. Rock Mass Rating (RMR) was determined for each quarry using UCS values and other field data obtained at the site. Explosive consumption and drilling records for recent six month were obtained from each quarry for the calculation of powder factor. Powder factor was plotted against each selected rock property and regression analysis was performed on test results to understand their standalone influence. The only realized best fitting model for the Powder Factor was AIV according to the regression analysis and it is very closely following the quadratic model. Rock property test results and past records of few other quarries were used to validate formulae obtained in this research. Explosive cost and production cost of all the quarries analysed for the same six months period. Results revealed that the production cost is a function of explosive cost since other costs on drilling, machineries and labour are usually incur relatively fixed costs in nature. Hence it can be concluded that the aggregate rock properties, especially Aggregate Impact Value (AIV) influence on powder factor of blasting and furthermore affects economics of the quarry production. More importantly, combined formula derived in this research can be used predicting powder factor of a fresh rock before conducting any blasting activity.