National Mineral Resources University—Mining University, Saint-Petersburg, Russia:

A. G. Protosenya, Head of a Department, Doctor of Engineering Sciences, e-mail: kaf-sgp@mail.ru
A. N. Shokov, Researcher, Candidate of Engineering Sciences

The article addresses a topical problem of calculating parameters of pillars in room-andpillar ore mining. It is suggested to use 3D modeling based on finite element method to predict stresses and strains in rocks. The developed 3D model of extraction of four blocks in an ore body allows accounting for the sequence of stoping, effective non-equicomponent gravitational and tectonic stress field, thickness and dip angle of the ore body, deformation and strength characteristics of enclosing rock mass and parameters of various purpose pillars. By way of illustration, the authors discuss an alternative method used in Nyurpakkh apatite-nepheline mine on the Kola Peninsula. On the assumption of preset pillar parameters, effective stresses and the related safety factors are calculated. It is revealed that the standard procedure in use to calculate room-and-pillar method parameters based on admissible spans of exposures yields overestimated values of safety factors for pillars and pillars are oversized as a result. In the framework of the proposed approach, the authors have reduced the cross section area of isolated interchamber pillars and the width of a crown (or inter-panel) pillar. In prospect, this universal finite-element model can assist in selection of room-and-pillar method parameters as function of depth of mining and variation in gravitational-tectonic stress field, which will enable optimization for size of various purpose pillars and will ensure safe mining.

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