In Block Caving drawbells allow for flow of broken rock. The drawbell construction starts with a drawbell design, which is constrained by the extraction layout shape and development drives sizes. The resulting shape of the drawbell is highly influenced by drilling performance, particularly drillhole deviation. This paper presents the results of a comprehensive analysis of drillhole deviation data undertaken from more than 2,000 holes of 76 mm diameter, having an average length of 12 m and drilled in more than 500 ring positions. In terms of drawbell design, the analysis indicates that the holes less affected by drillhole deviation are those with plunge angle ranging between 65° to 90°. Those holes are located near the centre of the drawbell. The holes less inclined show more deviation. They correspond to those forming the edge of the drawbell shape. Therefore, these areas can be exposed to possible blast damage due to confined charges. The analysis also indicated that 59% of the measured points have a drillhole deviation percentage (DD%) greater than 2%, while 2% of the points present a DD% over 10%. An industry standard for drawbell drill deviation along drilled depth was developed as a tool to check the effectiveness of a blast design, in terms of drill patterns that are likely to appear due to drillhole deviation.

In primary rock mass, with high intact strength and a small or null presence of open discontinuities, the rock mass strength depends on the volumetric distribution and mechanical properties of veinlets filled with different minerals. Vein properties can be used to obtain an index for rock mass characterization and classification into geotechnical domains, or they may be used directly in wedge analysis or in complex numerical models. A mineralized vein presents shear and tensile strength. These properties were measured, and the scale effect was approached by using 150 mm diameter samples for direct shear and indirect tensile tests. Vein properties were also obtained from triaxial compression tests in 48mm diameter samples. The test methods used are analyzed and the values of the mechanical properties of veinlets per mineralogy are given.

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.