Saint-Petersburg Mining University, Saint-Petersburg, Russia:

A. D. Kuranov, Head of Laboratory, Candidate of Engineering Sciences, Kuranov_AD@pers.spmi.ru
I. I. Bagautdinov, Senior Researcher, Candidate of Engineering Sciences
D. A. Kotikov, Senior Researcher, Candidate of Engineering Sciences
B. Yu. Zuev, Head of Modeling Laboratory, Candidate of Engineering Sciences

The Yakovlevo deposit of rich iron ore is located in the Belgorod Region. The deposit is composed of two genetic ore types—rich iron in residual soil of ferruginous quartzite and sedimentary ore. The rich ore occurrence depth is 440–550 m. The thick sedimentary formation contains 5 aquifers. The sedimentary roof is loose and unstable rocks. One of the major engineering problems in the mine is prediction of the safety pillar subsidence in the course of stoping. The pillar is the impervious stratum and protects the mine from excess ingress of groundwater. Over the period from the observation beginning and up to 2016, the pillar subsidence amounted to round 1470 mm. The ground surface subsidence was not less than 900 mm. The procedure developed for the subsidence prediction in the safety pillar consisted of three independent stages of laboratory and in situ research. In the first stage, the comprehensive finite-element model of the Yakovlevo Mine was prepared. Subsidences were calculated by the finite element method in the licensed software package RS2 of Rocscience. The comparative analysis of the calculated and in situ measured data showed their acceptable agreement. The numerical model parameters were verified. In the second stage, the physical modeling of all strata and their movement was carried out with equivalent materials. The modeling procedure was based on solution of problems on rock mass movement using two different-scale models. From the modeling results, it is found that the extreme subsidence of the safety pillar in sequential toping makes 3.17 m. In this case, the flexure of the lower boundary of the water-tight stratum is within the critical values. The results were confirmed by the analysis of photographic material showing no visible (water-conducting) fractures. Based on the numerical calculations, physical modeling with equivalent materials and the in situ data analysis, the prediction of the safety pillar subsidence was carried out for stoping operations down to –425 m. During extraction of bottom layers (from –410 to –425 m), the flexure and deformation in the water-tight stratum roof reach critical values.

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