PSI - Issue 32

E.A. Gubanova et al. / Procedia Structural Integrity 32 (2021) 42–48 E.A. Gubanova / StructuralIntegrity Procedia 00 (2021) 000 – 000

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undermined facilities located on the earth ’s surface. The paper deals withstudying the earth surface above the mine openings. During the deformation of the salt rock under the influence of the stoping, a displacement trough of the earth surface is formed. The pillar mining system has interchamber pillars of varying degrees of stability, which allows for a smooth lowering of the rock pack, serves as a waterblocking stratum and is located between the top of the upper layer being mined and the bottom of the first aquifer from the bottom. The stress-strain state of the rock mass determines the stability of the pillars. In case of their limited service life, starting from a certain point in time, the deformation of the pillars occurs at increased rates. A high rate of destruction determines the laws of the distribution of rock deformations in the boundary part of the shift trough. In case of a significant value of the subsidence rate or the loading degree of the interchamber pillars, a steep edge part of the shift trough is formed with significant deformations of the earth ’s surface, which results in the activation of the undermined rock subsidence and the formation of zones of subvertical cracks, dangerous in terms of the rock mass discontinuity. The activation of the displacement process at the level of the earth ’s surface also leads to a significant increase in horizontal and vertical deformations, which can lead to the destruction of facilities located on the earth ’s surface. The steeper the edge part of the displacement trough, the higher the level of technogenic load influences the undermined mass. The development of the Verkhnekamskoye field is characterized by a wide variety of mining-geological and mining technical factors (different depths and thicknesses of productive strata, development parameters and time of stope excavation, anomalous structure of the waterblocking stratum, etc.), which is realized in a variety of forms of the displacement of the surface of the earth. It is obvious that the destruction of salt rocks, in particular, due to a decrease in the bearing capacity of the interchamber pillars of productive formations, can also take place at an earlier stage of the mass deformation. Thus, for a more detailed study of the state of the undermined strata and obtaining a reliable current and adequate predictive estimation of the geomechanical situation, it is necessary to perform a retrospective analysis of the deformation of the salt mass as one of the effective ways to determine the location of areas of technogenic destructions that could have formed within the studied area up to the present time. In addition, such formed disturbance zones do not disappear anywhere afterwards. As a consequence, in subsequent predictive calculations of discontinuities in the undermined rock mass without taking into accountthe previous years of its deformation, we have overestimated values of its stability and overestimated values of the safety of the mine’ s operations. In the Verkhnekamskoye deposit of potash and magnesium salts area, mining operations are carried out on three sylvinite layers, a carnallite layer and a rock salt layer in various combinations. An increase in the depth of mining operations, an increase in the extraction of minerals by increasing the span of the chambers and reducing the width of the interchamber pillars often lead to serious negative consequences. A retrospective geomechanical analysis makes it possible to minimize the risks of emergency situations and resolve in a timely fashion the issue of the need to apply certain additional measures to protect the undermined rock strata and avoid anyflooding of the mine. 2. Calculational Methods In mathematical modeling, the estimation of the level of destruction of the salt mass was carried out in a two dimensional elastoplastic formulation for the plane strain state according to the requirements of the "Guidelines for the protection of Mines from Flooding and Protection of Undermined Facilities in the Verkhnekamskoye deposit of potash and magnesium salts" by Instructions(2014). In the design scheme, the mined-out space is represented by a medium with lower property values of the corresponding layer rock. The degree of the reduction of properties was found using the actual and design parameters of the mining system. To describe the development over time of displacements of thetrough, a rheological approach was used, based on the mathematical description of the graphs of the increase of subsidence in the earth ’s surface by Amusinand Linkov(1974). Then, based on the modification of the method of alternating elastic moduli known in rheological analysis by Baryakhand Samodelkina(2005), the alternating modulus of the extracted seam will be determined by the recovery factor from the seam, the modulus of rock deformation and the creep function by Amusinand Linkov(1974). The modification is different as the alternating moduli characterize the deformation of not all elements of the geological section, but only the extracted layer. When mining several layers, the corresponding parameters (recovery factor, rock deformation modulus, creep function) are taken into account for each of them. At the same time, the change in the deformation moduli over time is fully determined by the graphs of the increase of subsidence in the earth ’s surface, which help to estimate the integral rheological parameters of the undermined mass using a mathematical processing by Baryakhet al. (2005). The criteria-based estimation of the degree of changes in the state of the undermined mass during the