A Heuristic Methodology for Economic and Geomechanical Optimization in Sublevel Open Stoping Mining Method

The top-down extraction sequence in the sublevel open stope method leaves rib pillars to support the excavations, so the stability of the pillars and stopes makes dilution control critical in this method. This work introduces an integrated methodology for the net profit and geomechanical optimization of the layout of open stopes and rib pillars with the use of a genetic algorithm. Parameters such as the minimum size of stopes, minimum size of pillars, maximum accepted dilution, and maximum acceptable percentage of pillar failure need to be informed by the user. A profit function capable of attributing economic value to the geometric set analyzed, including the geomechanical performance, is established. The geomechanical performance of the geometric sets is obtained by autonomous numerical models in the FLAC3D software and includes the average percentage of pillar failure and the potential dilution. The algorithm is verified using a case study of a mining panel of an underground gold mine with a top-down mining sequence. An 8% increase in net profit was obtained relative to the engineer’s design method, considering 70% of hangingwall support efficiency for both methods. The percentage of pillar failure decreased threefold. When considering no hangingwall support, the net profit increase is 22% relative to the engineer’s design method. The proposed methodology proved that it is possible to carry out an integrated optimization, considering the costs inherent to mining and the cost of the geomechanical performance, reducing the need for secondary support compared to the engineer’s methodology.