Statistical analysis of the impact of ore draw strategies on wet inrush hazard susceptibility in a panel cave mine

Abstract

Inrush hazards involve a sudden inflow of material into an underground mine excavation. In a cave-mining setting, this typically involves high amounts of fine-grained material and water flowing from an extraction-level drawpoint. Operations encountering these hazards have developed tactical and strategic risk management plans to address the risk posed to mine safety and production. These plans have improved over time in meeting safety requirements owing to the utilization of evolving automated systems. However, managing the impact of inrushes on production rates has remained an area of improvement, particularly in mature caves with high quantities of fine material and stored water. In such conditions, understanding the impact of draw strategies on inrush susceptibility is particularly important to guide a risk-informed draw optimization strategy, with the goal of minimizing spill frequency while maintaining target production rates. In this study, the impact of draw strategies on inrush susceptibility was assessed through the statistical analysis of draw and spill history at PT Freeport Indonesia's Deep Ore Zone mine. Two draw-related variables were used for quantification of draw strategy: Draw Rate and Differential Draw Index. Differential Draw Index is a new parameter developed in this study to quantify draw non-uniformity, with the aim of capturing the impact of differential draw rates on inrush susceptibility between neighboring drawpoints. The results from this study show that Draw Rate and Differential Draw Index should be considered concurrently when assessing the impact of draw strategy on inrush hazards. An up to 8-fold increase in spill probability was observed when both Draw Rate and Differential Draw Index were in their upper ranges, compared to when either of these variables was in its lower ranges. The results also showed that if a drawpoint had a long-term history of isolated draw, it was more susceptible to inrush under short-term non-uniform draw.