Issue 49

A. Baryakh et alii, Frattura ed Integrità Strutturale, 49 (2019) 257-266; DOI: 10.3221/IGF-ESIS.49.25 265 The boundary conditions are specified as follows: the upper boundary is free, at the side boundaries the horizontal displacements are equal to zero, the lower boundary has vertical displacements reflecting the deformation of the top of the upper mined bed as a result of mining operations (Fig. 3.). It is very important that these displacements were obtained as the result of mine geodetic measurements and characterize the real deformation processes in the mined mass. The initial stress of the undisturbed mass was taken to be lithostatic. In this case , 0 y H    ,   0 1 x H       where  is the specific weight of rocks, H is the mining depth. Additional stresses were determined by solving the initial problem. The stresses were expanded into a Fourier series, in which 60 harmonics of their symmetric part were retained. The number of the unknowns in the algebraic analog of the problem was 2280. A specific feature of rocks, containing salt strata, is low values of ultimate tensile strains [12], which at the average is 0.1- 0.2% and serve as the indicators of the formation of subvertical cracks in the salt beds [13]. The presence of the through tension zone with horizontal strains exceeding the threshold values for saliferous rocks is indicative of the risk of discontinuity in the waterproof stratum and ingress of fresh waters into mine openings. The distribution of horizontal tensile strains is illustrated in Fig. 4. The obtained results are in good agreement with empirical data on the crack formation in the layers of mined rock strata [13]. Figure 4 : Distribution of horizontal tension strains in the mined-out mass C ONCLUSIONS n this study, we demonstrated the efficiency of the proposed semi-analytical scheme of the finite element method for assessing the changes in the state of the layered rock mass under the conditions of underground mining based on a rather simple computational algorithm. At the same time, the degree of the impact of mining operations on the rock mass is determined by the boundary conditions and can be generally estimated using the field measurements. Utilization of an actual survey data in geomechanical calculations provides higher validity of waterproof stratum stability estimations and is applied successfully for prompt analysis of mining safety. A CKNOWLEDGMENTS his work has been financed by the Russian Science Foundation (grant No. 19-77-30008 ). R EFERENCES [1] Baryakh, A.A., Asanov, V.A., Samodelkina, N.A., Pankov, I.L., Telegina, E.A. J. (2013). Geomechanical provision of protection of potassium mines from flooding. Gornyi Zhurnal. 6, pp. 30-34. I T