The MMP Mechanised Mining Systems Programme is advancing safer and more efficient multi-reef mining through the use of advanced numerical modelling for pillar design.

This approach provides critical insight into how stress develops within rock formations, enabling more informed extraction planning that protects workers and optimises performance in complex, multi-reef environments.

The study analysed three real-world mining scenarios to better understand how stress behaves under different conditions.

The first case looked at mining the Upper Group 2 (UG2) reef beneath previously mined Merensky Reef stopes. Decades of Merensky extraction left irregular rock remnants, creating unpredictable high-stress zones in the underlying UG2 pillars. Standard pillar design methods cannot account for these variations, increasing the risk of pillar failure or rock bursts. Numerical simulations helped identify these high-stress areas, highlighting where additional support or modified layouts may be needed.

The second case focused on shallow Middle Group 2 (MG2) reefs mined above older MG1 stopes. While pillar stresses were generally low, making the layout relatively stable, stress levels varied widely across pillars. This demonstrates that conventional design formulas, such as tributary area theory, may not provide reliable results. This reinforces the importance of continuous monitoring and assessment, even in shallow mining areas, to maintain safe conditions.

The third case investigated multi-reef bord and pillar layouts with very small reefs. Simulations revealed complex interactions of some pillars experienced increased stress, while others were relieved, depending on their position relative to mined-out areas. Non-aligned, or non-superimposed pillars were identified as potential zones of instability, showing that careful pillar placement and sequencing are crucial for safe multi-reef mining.

From these case studies, practical guidelines emerged for multi-reef mining operations:

• Use numerical modelling to understand stress patterns and design pillar layouts tailored to site-specific conditions. Traditional single-reef methods are not sufficient.
• Plan mining sequences carefully, avoiding simultaneous extraction across reef horizons unless fully controlled and monitored.
• Barricade old workings on other reef levels to prevent unexpected collapses.
• Monitor pillars and middlings with instruments to track stress changes and validate modelling assumptions.
• Superimpose pillars where possible to promote balanced stress transfer and provide extra support for large spans or high-stress areas.

The Rock Engineering Pillar Design study highlights the value of understanding underground conditions before making design decisions. As mining moves into deeper and more complex reef systems, these findings provide a roadmap for creating safer and more efficient layouts. By applying these strategies, Multi-reef Extraction can continue extracting valuable resources while protecting workers, equipment, and the long-term stability of their operations. With the right combination of technology, planning, and monitoring, multi-reef mining can move from being unpredictable to safe, sustainable, and highly productive.