Research Center for Geomechanics and Mining Practice Problems, Saint-Petersburg Mining University, Saint-Petersburg, Russia:

M. A. Vilner, Researcher, Candidate of Engineering Sciences, Vilner_MA@pers.spmi.ru

Apatit’s Division in Kirovsk, Kirovsk, Russia:
A. A. Streshnev, Head of Rockburst Prediction and Prevention Service
V. S. Onuprienko, Chief Engineer

A pillar established between drilling-and-haulage drifts is one of the key elements in sublevel caving system. The currently common procedure of determining such pillar parameters is the collation of the load-bearing capacity of the pillar with the effective stresses. This procedure omits many factors intrinsic to apatite–nepheline ore deposits. The pillar stability maintenance via the integrated stress–strain behavior prediction ensures safety of mining operationы and reduces the need of re-installation of support systems in underground openings, which directly influences mining efficiency. The authors infer on the main disadvantages of the current approaches to stability estimation of rock pillars in apatite–nepheline ore mining. It is found that rock pillar stability at such deposits should be considered as local and global stability. The local stability is inspected visually by observations over geomechanical processes in the adjacent rock mass of the pillars. A possible loss of the global stability should be substantiated by instrumental observations or modeling. The implemented numerical modeling allows drawing a conclusion that the stress state of pillars is mostly affected by: the stress state of the adjacent rock mass of a pillar before it is drilled around and at the stage of enveloping the pillar with stopes; the rock strength; the pillar geometry (shape and dimension); the position and advance direction of the stoping operations relative to the pillar. The numerical modeling provided the stress–strain analysis of pillars with regard to the weightiest factors—tectonic stresses, higher-level stoping and pillar geometry. The accomplished research revealed stress–strain patterns in pillars, and made it possible to offer recommendations on optimization of pillar parameters.

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