PSI - Issue 32

A.A. Baryakh et al. / Procedia Structural Integrity 32 (2021) 17–25 Baryakh A.A / Structural Integrity Procedia 00 (2021) 000 – 000

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The subsidence distribution at the earth’s surface at the moment of complete filling of the mined -out space with brines and their saturation with Na and K, during the planned liquidation, are shown in Fig. 4a. For the case of a possible emergency breakthrough of freshwater, the subsidence distribution is illustrated in Fig. 4b. The analysis of the obtained results resulted in the following conclusions. 1. During the planned flooding, there is increased subsidence in the western part of the potentially dangerous area (Fig. 4a) due to the degradation of the pillars (Fig. 1a). It should be noted that, as a result of these deformation processes, a displacement trough with a sufficiently high gradient edge is formed in this area, which predetermines an increase in the human-induced impact on the waterblocking stratum. 2. In the case of an emergency breakthrough of freshwater into the area at the eastern boundary of the site, and in contrast to the planned flooding,along with the dissolution of the salt rocks at the breakthrough site, there is a significant increase in subsidence in the western part (Fig. 4b). This is caused by the fact that the western part is located at lower elevations in relation to the east, and the main flow of the unsaturated brines is directed here. Risk analysis of the destruction of the waterblocking layer was carried out to estimate the possible violation of the waterproofing of the liquidated area, the emergency flooding of the entire mine and the formation of sinkholes on the earth’s surfa ce. The studies were based on the localisation of plastic zones, reflecting the formation of subvertical cracks in the formations that make up the waterblocking strata. In addition, the distribution of horizontal tensile deformations in the undermined mass was analysed, which qualitatively characterised the danger of destruction of the waterblocking layer. The value of 0.1% was taken as the ultimate tensile strain for the salt rocks.

Fig. 5. Discontinuities of the waterblocking stratum (WS) along the section I-I: (a) is the planned flooding; (b) is the emergency breakthrough of the freshwater.

Fig. 5. shows the discontinuity zones of WS along the most dangerous latitudinal section I-I, located near the waterproofing bulkheads under construction. As already noted, in the western part of the potentially hazardous area, a shear trough is formed wit h high gradients of subsidence of the earth’s surface in the western marginal part. In the presented results, it can be seen that by the end of the planned flooding, the discontinuity zone only covers the lower part of the waterblocking layer (Fig. 5a). In general, its bearing capacity is ensured. In case of an emergency breakthrough of the freshwater (Fig. 5b), a discontinuity in the waterblocking layer is predicted in this area, along with all the associated negative consequences. 4. Conclusions The possibility of estimating the negative consequences associated with the elimination of a potentially dangerous area has been shown by using the integrated filtration-migration and geomechanical numerical modelling. According to the performed calculations, we localised the zones within which the liquidation causes an increase in the human-induced impact on the waterblocking stratum and creates a threat of destruction. To minimise the discontinuity risks of the waterblocking layer in the submerged western part of the potentially hazardous area, it is recommended that saturated brines are used to fill it. These measures will make it possible to reduce the degree of dissolution of the salt rocks in this area and to reduce the human-induced impact on the layers of the waterblocking stratum. Acknowledgements