Investigating the causes of rock overreach during blasting operations

Abstract

Backbreak or overbreak: This is when the rock mass behind the row of blastholes farthest from the face is broken or cracked. Roko construction stone Quarry is located in Nakagere Village, bukerere sub county, mukono district (Uganda) ROKO construction quarry limited is a surface mine applying bench drilling and blasting and its operations being affected by one of the most issues associated with the blasting, backbreak/overbreak. The quarry consists of five stable benches those of 10m, 15m,7m, 9m and 8m. These benches have high Q value ranging from (49.675-49.125) the Q system rock mass rating for the upper benches and for the lower benches are slightly weathered and high UCS ranging from (112- 200Mpa) and (50-80Mpa) range for upper benches The holes have a diameter of 50mm, subdrill of 0.8m and blasthole depth varying with the bench height, the holes are drilled vertically at a spacing of 2.1m, 1.6m burden Generally, the quarry has a strong rock favouring stability despite for the first row of each bench Although the design powder factor is 0.37 according to the research it increases to 0.46 which is within the range of hard rock blast but corresponding to small spacing and burden These research addresses the cause of backbreak/overbreak after the investigation on the geological properties, drilling and blasting parameters, assessing of the rock strength and statistically analyzing the data using multiple linear regression method in SPSS