Geotechnical analysis of blasting sequence and resulting shapes of drawbells in block cave mines

ABSTRACT Drawbells allow disassembled ore to be extracted from the production levels in block cave mines. As part of the construction process, blast damage must be minimised, enabling the remaining rock mass surrounding the drawbell to sustain the induced stress during the different stages of a block-caving operation for a successful mine plan extraction and ore recovery.This paper proposes two approaches for the geotechnical evaluation of drawbell blast performance. Initially, the expected dynamic burden is calculated along the length of the blasthole and used to assess surveyed blast holes. Secondly, the design compliance is evaluated using the Radial Distance of Over/Underbreak concept, which compares designed and scanned shapes relative to height and radial orientation.The results have identified confined blast zones at the top and around the corners of drawbells. Excessive confinement may cause damage to the pillars and negatively impact the stability of the production level.