Application of laser scanning to measure fragmentation in underground mines

The particle size distribution of fragmented rock in mines significantly affects operational performance of loading equipment, materials handling and crushing systems. A number of methods to measure rock fragmentation exist at present, however these systems have a number of shortcomings in an underground environment. This paper outlines the first implementation of high resolution 3D laser scanning for fragmentation measurement in an underground mine. The system is now used routinely for fragmentation measurement at the Ernest Henry sublevel-cave mine following extensive testing and calibration. The system is being used to study the effects of blasting parameters on rock fragmentation to optimise blast design. Results from 125 three dimensional scans measured the average P50 and P80 to be 230mm and 400mm respectively. The equipment, methodology and analysis techniques are described in detail to enable application of the measurement system at other mines. Introduction Rock fragmentation by blasting affects the efficiency, productivity and cost of downstream operations including loading, crushing and grinding (Dinis da Gama, 1990; Scott et al., 1999). In addition, the particle size distribution of rock fragmented by blasting is known to influence gravity flow and ore recovery in sublevel cave mines (Laubscher, 1994; Power, 2004). Various gravity flow studies have demonstrated the size of fragmented rock has a direct effect on draw zone geometry and flow mechanisms (Kvapil, 1998; Power, 2004). Larger rock fragments result in larger draw zones and more favourable recovery conditions (Laubscher, 1994), but can lead to dangerous and costly blockages called 'hang-ups'. A number of studies have identified that the size distribution characteristics of fragmented rock has an influence on loading equipment productivity, including the loading cycle time and bucket payload (Allen et al., 1999; Brunton et al., 2003; Narendula, 2004). Overall, the particle size distribution of fragmented rock in a sublevel cave mine (SLC) mine has an effect on most aspects of operational performance. Commonly used image base systems for fragmentation measurement have a number of limitations when used underground such as lighting, dust, water and colour which affect particle delineation. Due to the critical importance of fragmentation, a measurement system was required that was accurate, automated, fast, low cost and could be conducted safely at a cave draw point. Using one of the mines existing high-resolution 3D laser scanning systems, a measurement and analysis strategy was implemented, tested and configured in an underground mine at the Ernest Henry Mine (EHM). This system was used …