Deformations and fracture of rock strata during deep level potash mining

Abstract

Increased mining depths entail both increased rock pressures and complicated rock mass structures. When it comes to mining mineral salts, there is a significant difference in the strength and deformation properties of rocks developed in the geological section, which affects the nature of deformation and the destruction of underworked strata. During the initial development stage of the Gremyachinskoye deposit, where the mining of potash salts at depths of more than 1,000 meters has been planned, a mathematical model of the undermined mass has been developed, reflecting the main features of its geological structure and the design parameters of a pillar mining system. The mathematical modelling estimated safe conditions of undermining the waterblocking strata and the expected deformations at the earth’s surface. This was carried out with an elastic-plastic plane formulation using the finite element method. The time factor was accounted for based on the developed modification of the method of alternating deformation moduli. Based on the mathematical modelling performed, it was shown that geomechanical models of new deposits of potash salts being prepared for development can be calibrated using the information available from analogous deposits; this information can be subsequently corrected, reflecting certain differences in the geological structure and parameters of the mining system. Based on the numerical modelling results, an increase in the boundary angle of the subsidence trough of the earth’s surface was established due to the significant depth of mining and the presence of hard rock strata in the geological section, which allowed the linear dimensions of the protective pillars under critical facilities to be reduced, alongside minimising losses of potash ore.