Paper contribution

Optimal Stoping Limits, Stability, and Dip Pillars for Seismicity: SA Gold Mine

Richard Masethe; Onke Vetman; Thuthukani Sibiya

Proceedings
EUROCK 2026
Pages
201-212
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

This study integrates two critical geotechnical investigations conducted at a shallow gold mine in South Africa, focusing on optimal stoping limits, ground stability, and the effectiveness of stabilizing dip pillars within broader seismicity management strategies. The first component evaluates the optimal stoping limit for the 202 N S1 Raise Line to minimise abutment stress on the underlying 202 N Returned Air Way (RAW). Geological complexities including major faults dipping 65° and 85° south, minor discontinuities, and an over-excavated section measuring 4.4–4.8 m necessitated a rigorous assessment of ground stability. Numerical modelling using IMS Vantage tested stoping spans of 5 m, 10 m, and 15 m to determine their impact on the Rock Condition Factor (RCF). Although a 15 m span produced the most favourable stability conditions, it was economically unviable. The 10 m stoping limit emerged as the optimal compromise, with localised instability addressed through a combination of resin-grouted bolts, mesh, lacing, and shotcrete to mitigate Fall of Ground (FOG) risks. The second component investigates the performance of 15 m stabilizing dip pillars, introduced in 2020 to manage seismicity, which nevertheless continued to escalate by 2023 with increasing Seismic events of ML ≥ 2.0. These seismic events produced damaging rockbursts that threatened safety and disrupted production. Analysis revealed limitations in the dip pillar design and inconsistent adherence to seismicity management principles, including bracket pillar placement and lead-lag formation. Comparative assessments of Average Pillar Stress (APS), face stress, closure rates, and seismic response between compliant and non-compliant mining areas highlighted the need for improved pillar configurations. Overall, the research underscores the importance of optimised stoping spans, robust support strategies, and strict compliance with seismicity management principles to enhance ground stability, reduce seismic hazards, and sustain safe, efficient production at shallow gold mine.

Contributors

Authors

  1. Richard Masethe University of KwaZulu Natal, South Africa ORCID 0000-0002-4420-7885
  2. Onke Vetman University of KwaZulu Natal, South Africa
  3. Thuthukani Sibiya University of KwaZulu Natal, South Africa

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