Abstract
• The drilling errors of manual jumbos are 1.3% for the level and 2.1% for the ramp. • There is a direct nonlinear negative correlation between the rockmass and overbreak. • Computerized jumbos have possessed greater drilling accuracy than manual jumbos. • Below Q-value 10, the region may define as constructional and geological overbreak. • Beyond Q-value 10, the region may designate as a zone of constructional overbreak. Overbreak in underground excavation is one of the undesirable outcomes that may emerge from many quality-compromising events. Among these, the drilling and blasting generally are one of the most important contributing parameters. This paper focuses on the study of drilling inaccuracy in manual drilling operations and the contribution of geological discontinuities to overbreak. A total of 855 blasts were conducted using conventional manual jumbo and computerized semi-automatic jumbo in different rock mass conditions wherein RMR varied from 45 to 75 and Q-value from 0.46 to 45. This was done to investigate the influence of rock mass quality on overbreak in underground drivage. From the study, it was found that 2.1% and 1.3% of overbreak tend to cause due to manual drilling inaccuracy of ramp and level drivages, respectively. Besides, the geological discontinuities have an effect on overbreak upto the Q-value 10 and this may be termed as geological and constructional overbreak. Above the critical point (Q-value 10) in the rock mass scale, the region may be termed as constructional overbreak due to the only presence of constructional error.
Published Version
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