PSI - Issue 32

A. Yu. Shumikhina et al. / Procedia Structural Integrity 32 (2021) 224–229 A.Yu. Shumikhina/ Structural Integrity Procedia 00 (2019) 000–000

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the plastic deformation regions in the WS. The mathematical modelling results were compared with the seismic survey data, in terms of the position of the identified geophysical anomalies. If they did not comply, the strength properties of the rocks were changed, and the calculations were repeated. The final stage of the iteration cycle was the selection of such strength characteristics of the salt rocks that provided the spatial coordination (laterally and vertically) of the plastic deformation zones and estimated wave anomalies. The implementation of this approach within an iterative procedure (2) made it possible to directly determine the decrease of the mechanical properties of the salt rocks during the computations and to estimate a degree of the continuity preservation of the WS strata. 3. Results Now, great experience has been accumulated in the use of the seismic-geomechanical control method at the mines of the Verkhnekamskoye potassium salt deposit. The application of the developed method on the example of the eastern part of the mine field of the Solikamsk potash mining deposit (SPMD) of PAO Silvinit was illustrated. In the mathematical modelling, the main characteristics of the undermined mass structure, the action of mass forces, and intensity i γ ( i γ is the specific weight of the rocks of the i -th element of the geological section) were considered. The boundary conditions were formulated based on the following considerations: the upper boundary (day surface) was taken as a free one; at the lower boundary, the vertical displacements were considered equal to zero, and at the side boundaries, the horizontal displacements were considered equal to zero. The mined space was modelled by a medium with properties that were lower in relation to the rocks of the corresponding strata. The reduction of mechanical properties was estimated by the actual parameters of the pillar mining system. The anomalies identified after the seismic exploration were reflected in the calculations as areas with reduced mechanical properties of the salt rocks. By using the general geological considerations and preliminary geomechanical calculations, the anomalies were classified as both natural and man-induced ones. To reflect the naturally weakened zones identified according to the results of the seismic explorations, the field of additional stresses which was caused only by the mining operations was calculated during the mathematical modelling. The initial vertical stress along the entire section, including the weakened zones, was taken to be equal to H γ . The integral parameters of the creep of the undermined mass were estimated according to the data of the mine surveying along the profile line No. 5 of the SPMD -1. Figure 2 shows the subsidence of the earth’s surface along the calculated profile. There is quite an acceptable agreement between the actual and calculated subsidence values, which indicates the adequacy of the mathematical modelling results compared to the real deformation processes. The formed displacement trough fully reflects the implemented mining parameters. As can be seen from the presented results, within the calculated profile at the current time, the maximum subsidence of the earth’s surface (3.6 metres) was formed within block 151. The steepest gradient of subsidence of changes was observed at the eastern boundary of block 183 and on the boundaries of blocks 51 and 49. To a certain extent, their presence was associated with the weakened zones (I and III) located here, localised according to the results of the seismic exploration. A quantitative estimation of the subvertical fracture formation in the WS layers was carried out according to the Mohr-Coulomb criterion within the elastoplastic approach considered above. As already noted, the results of the seismic surveys were used to parametrically adjust the geomechanical model. For this, by reducing the strength and deformation properties of the salt rocks, the spatial correspondence of the areas of plastic deformation (disruption of the WS continuity) to the identified wave anomalies of the natural and man-induced genesis was ensured. The geomechanical calculations showed that changes in the strength properties of the salt rocks within the geophysical anomalies in a reasonable range did not significantly affect the final criterial estimations of the safe undermining conditions of the WS.