Perm National Research Polytechnic University, Perm, Russia

Yu. A. Kashnikov, Head of Department, Doctor of Engineering Sciences, Professor, geotech@pstu.ru
S. G. Ashikhmin, Doctor of Engineering Sciences, Professor

Yakovlevsky Mining and Processing Plant (GOK), Yakovlevo, Belgorod Region, Russia
D. V. Golubnichiy, CEO
D. Kh. Gilyazev, Head of Hydromechanical Monitoring Services

In the Technical Project for the development of iron or es at the Yakovlevskoe deposit, safety measures have been designed to prevent water breakthrough from the un-dewatered Lower Carboniferous aquifer during extraction of rich ores using a descending horizontal layer system with backfilling. These measures include leaving a protective pillar of ore mass with a thickness of 65 meters under the water-bearing Lower Carboniferous horizon at a level of -300 meters, creating an artificial protective ceiling in the upper part of the minedout level using higher strength backfill, and conducting descending layer extraction of ore with full backfill of mined-out space using hardening mixtures. The results of long-term instrumental observations of the surface and underground benchmarks in the main blocks indicate that the measured soil subsidence above the protective pillar exceeds the projected values by 4–7 times (correspondingly, the actual effective thickness exceeds the projected one). To clarify the reasons for this phenomenon and to assess the current stress–strain behavior of the rock mass and the condition of the water protection pillar, a large-scale 3D geomechanical model was developed. Its parametric framework was based on the results of instrumental observations and tests of the physical and mechanical properties of rocks and ores. The base mechanical model of the ore mass was adopted to be the Mohr–Coulomb elastoplastic model with softening, including parameters governing the nature and degree of strength reduction in the course of development of plastic deformations, in addition to standard indicators. The modeling results clarified the current situation and allowed the prediction of the maximum water inflows into the mine as mining operations continued.

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