College of Mining, NUST MISIS, Moscow, Russia:

V. A. Eremenko, Director of Research Center for Applied Geomechanics and Convergent Technologies in Mining, Professor, Doctor of Engineering Sciences, prof.eremenko@gmail.com

The presented research findings are aimed to justify feasibility of reinforcement of deformable rib pillars in a salt mine by rock bolts with determination of the rockbolting pattern characteristics towards geomechanical stability of the mine for a period of 2018–2032. The rock mass quality calculated by Barton’s classification for a salt rock mass subjected to mining with blasting in the last century makes Q’ = 39, which means the rock mass is unbroken and stable. The roof in the stopes extracted 40–50 years ago is stable; detachment of rocks is observed at the bottom of the rib pillar to a depth to 0.5–2 m from the exposure and to a height of 0.5–5 m from the floor; local damages are accompanied with separate rock falls; it is allowed to leave the exposures unsupported. Based on the numerical stress–strain analysis of the rib pillar, given extraction of all stopes on three levels, it is found that: the minimum strength factor of the rib pillar is SF = 2.3; the maximal principal stress σ₁ in the rib pillar v ries as 6.7 to 7.6 MPa (at the top), as 7 to 9 MPa (in the middle), as 7.2 to 8.1 MPa (at the bottom), as 9.4 to 12.2 MPa (in the bottom edges—maximal values) and is less than the maximal allowable stresses for rock salt; the minimal principal stress σ₃ in the stope walls) ranges from 2.6 to 3.9 MPa (at the pillar top), from 0.1 to 3.1 MPa (in the middle of the pillar), from 2.9 to 4.2 MPa (at the pillar bottom) from 1.4 to 2.1 MPa (in the bottom edges of the rib pillar—maximal values) and is reflective on no intensive stress relaxation (potential stratification of wall rocks). The initial variant of the support design for the rib pillar assumed cable bolting. The implemented analysis revealed considerable disadvantages under the specific geomechanical and geotechnical conditions; inconvenience or impossibility of cable bolting to the required distance in the inclined boreholes as well as anchorage on the stope exposures (head of the bolts) because of the prohibited entrance in the stopes by the safety procedures; unattainability of the wanted yielding in view of the rib pillar deformation in the course of stoping (cable bolt rupture); high corrosive impact on strength characteristics of cable bolts. For the rib pillar, a special elastoplastic support system has been designed, including anchor bolts, hightensile MINEX mesh and friction bolts.
The author appreciates participation of R. V. Gramm, Technical Officer, Russol; D. V. Druzhkin, Director of the Sol-Iletsk Mine; RANK 2, Geobrugg and UralEnergoResurs companies, P. V. Volkov, Associate Professor of the Nosov Magnitogorsk State Technical University; M. A. Kosyreva, A. R. Umarov, A. M.Yanbekov and Ch. V. Khazhyylai, fellows of the Research Center for Applied Geomechanics and Convergent Technologies in Mining at the NUST MISIS’ College of Mining in this study.

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