Transitioning from Open Pit to Underground Mining: A Literature Review on Crown Pillar Stability

ABSTRACT: Driven by ever increasing mineral demand combined with the depletion of surface resources, the transition of mines from open-pit (OP) to underground (UG) operation is a proliferating phenomenon. These transitions are not inherently safe, several accidents have occurred at transitioning mines in recent memory. Crown pillar stability is a critical factor in ensuring the safety of a transitioning mine, as evidenced by the effects crown failures have caused in the past. Research on crown pillars in transitioning mines is significantly more scarce than that for entirely underground operations. This paper first briefly discusses existing design approaches for surface crown pillars before reviewing the relevant literature on OP-UG crown pillar design, monitoring, and failure. Several research gaps are identified, namely: numerical model verification, improved understanding of the effects of several variables, and the establishment of a parametric order of influence. To address these, field measurement-verified modeling to support empirical and analytical results, comprehensive numerical modeling to analyze factors such as rock mass quality and pore water pressures, and quantitative sensitivity analyses for the purpose of establishing an order of influence are proposed as future work.