Belgorod State University, Belgorod, Russia:

I. B. Agarkov, Senior Lecturer, agarkov@bsu.edu.ru
I. M. Ignatenko, Director of the Institute of Earth Sciences, Candidate of Engineering Sciences
V. A. Dunaev, Professor, Doctor of Geological and Mineralogical Sciences
I. S. Kryuchkov, Post-Graduate Student

This article presents the back-calculation data on bench deformations in open pit mine Zhelezny of Kovdor Mining and Processing Plant. The calculations are performed for 105 rock falls divided into six groups with respect to volume (m3): 0–200 is group 1; >200–500 is group 2; >500–1000 is group 3; >1000–5000 is group 4; >5000–10000 is group 5; >10000 is group 6. The computational method was the single-factor analysis of change in specific cohesion between the surfaces of deformation-limiting fractures. The internal friction angle is assumed to be constant as it is the least of all changeable and is correlatable with laboratory test data. Actual rock falls were simulated in GIS GEOMIX. The simulation correctness was ensured by the high-accuracy referencing and orientation measurements of fractures using 3D models constructed based on laser scanning and drone photography. For all sampled rocks, it is found that specific cohesion between fracture surfaces grows with increasing volume of rock falls. Specific cohesion in case of small volume rock falls (0–200 м³) in all types of rocks, except for olivinite, is approximately the same and ranges as 0.0021–0.011 MPa; for olivinite, this value is higher by 20 % at least. Higher rate slipping along fractures is typical of fenite (almost in all groups, specific cohesion is lower by 10–90 % than in other rock types), which is governed by supergene mineralization of fenites and by down water flow in fractures. The low and approximately equal values of specific cohesion (0.0058–0.0094 MPa) are observed in group 0–200 m³, which is conditioned by the action of blasting on deformation of benches.
The study is carried out under State Contract No. 075-03-2020-474/1 от 05.03.2020.

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