Examining the Effect of Powder Factor Variability on Granite Productivity

Abstract

This research seeks to examine the effect of powder factor variability on granite productivity during its quarrying. Schmidt hammer was used for the in-situ determination of rock hardness. Uniaxial compressive strength (UCS) of in situ rock was estimated from the values obtained from Schmidt hammer rebound hardness test and its density determined from laboratory test. After preliminary field studies, ten (10) blasts with varied powder factors were studied and their overall effects on granite productivity examined. Three (3) rock samples were carefully collected from the quarrying site and subjected to laboratory analysis for UCS and bulk density tests. With spacing and burden kept between 1.7 m and 1.8 m and stemming height also varied between 1.5 m and 2 m, charge columns of between 4.5 m to 6.5 m were maintained, while number of holes drilled per blast was between 64 and 88. Results obtained from the test revealed that the average UCS of the granite samples was 80.67 MN/m2 while the average bulk density was 2465.67 kg/m3. Therefore, considering ten (10) blasts with varied powder factors of between 0.77 kg/m3 and 0.97 kg/m3, total volumes of rock of between 1109.76 m3 and 2280.96 m3 was produced. Hence, varied powder factors have been found to have varying effects on rock fragmentation sizes and by extension, granite productivity.