One of the problems in ore mining is untimely preparation of ore reserves for extraction. Eventually, mining efficiency drops. Aiming to replenish quickly depleting reserves, mining of various-purpose pillars is undertaken. For this reason, studies into safe mining of pillars are relevant and essential. For instance, for a gold mine in ground conditions of pronounced geological and structural uncertainty, for the sustained short- and-medium-term production, a method was validated and proposed for extraction of ore reserves from the undermined crown pillar left under the open pit bottom. In the framework of this research, a geomechanical model of an ore deposit has been developed in the form of a conceptual flow chart of mining of a crown pillar under an open pit bottom at the preserved production infrastructure condition by surface and underground mining. 3D numerical modeling uses the finite element method. The calculations find that underground mining of the undermined protective pillar under the open pit bottom, due to considerable jointing of the steeply dipping ore body, is limited by expansion of wide possible rock damaged zones up to the ground surface.

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The current mining of thin and steeply dipping ore bodies features depth down to 700–1100 m below ground surface, increased dimension of various-purpose pillars and, as consequence, higher mineral loss and overall degradation of mining efficiency. In connection with this, it is urgent to find new mining systems as well as scientific approaches to validation of safe parameters of geotechnologies such that, depending on geological and geomechanical conditions, as well as on mineral value, minimize geotechnical risks and maintain competitiveness of production. The aim of this study is to determine safe parameters of open stoping technology for thin ore bodies in terms of the Irtysh complex ore mine. The key research methods are production planning and mathematical (numerical) stress–strain analysis and stability of structural elements in underground mines. The calculated parameters of pillars and stopes for open stoping ensure operating stoping in areas of steeply dipping or inclined ore bodies. Application of 3D mathematical modeling to geological and geomechanical conditions of an operating mine greatly expands the range of approaches and knowledge in complicated problem solving, which proves reliability and correctness of the results obtained for specific nonrecurring geotechnical situations.

The geotechnical situation in mines using the open stoping methods is governed by complex geomechanical behavior of rock mass around rib and level pillars. The impact of rock pressure on underground excavations grows in this case, and dynamic events due rock pressure happen more often. The latter became the reason for implementing this research. In terms of steeply dipping ore bodies, safe mining of earlier left pillars is feasible. The best scenario for pillar extraction, considering their parameters, is caving to open and partly filled with overlying rocks stopes. The geomechanical calculations during justification of mining parameters during extraction of ore reserves from pillars have determined regular patterns in the stress–strain behavior of rocks mass, which contributes to qualitative and quantitative prediction of safe and feasible mining conditions. The zones of instability in structural elements of the geotechnology, including pillars, are detected. The author proposes the order and sequence of pillar caving to open and partly filled stopes at the admissible completeness and quality of extraction.

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