PSI - Issue 32

M. Zhelnin et al. / Procedia Structural Integrity 32 (2021) 71–78

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M. Zhelnin/ Structural Integrity Procedia 00 (2021) 000–000

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Fig. 5. Distributions of the equivalent (a) and volumetric (b) plastic strains in the concrete shell and grouted sand

The predicted occurrence of plastic strains in the concrete shell after thawing is dangerous because of the possible shaft lining fracture during long term exploitation of the mineshaft. To prevent risks related to the destruction of the shaft lining, the parameters of the concrete shell has to be changed on the base of the limit stress criterion. One way of changing is to reduce its stiffness. Fig. 6 presents distributions of the equivalent and volumetric plastic strains for the concrete shell with the Young’s modulus reduced by 45%. In this case, there is no plastic strain in the concrete shell. However, the maximum values of the equivalent and volumetric plastic strains in the grouted sand have risen by 26% and 23%.

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Fig. 6. Distribution of the equivalent (a) and volumetric (b) plastic strains obtained with the reduced Young’s modulus of the concrete shell

Another way is to increase the thickness of the concrete shell. Fig. 7 shows distributions of the equivalent and volumetric plastic strains for the concrete shell with the thickness raised from 0.45 m to 2.47 m. The thickness of 2.47 m is the maximum possible value which can be provided during shaft sinking without damaging of the freezing wells. It can be seen that the small plastic strains occur only at the interface between the cast iron tubbing and the concrete shell. There are no plastic strains in the grouted sand. However, cement ground injection with this thickness can be carried out only after complete thawing of the frozen wall. Effect of the grouted sand thickness on the optimal parameters of the concrete shell is illustrated by Fig. 8. Fig. 8(a) shows change in the ratio of the optimal Young’s modulus of the concrete shell to the grouted sand modulus with the thickness of the grouted sand. Fig. 8(b) presents dependence of the optimal thickness of the concrete shell on the thickness of the grouted sand. The optimal thickness of the concrete shell is determined in such a way that plastic strains do not exceed maximum values presented in Fig. 7. It can be seen that with an increase in the thickness of the grouted soil layer the optimal Young’s modulus of the concrete shell rises and its optimal thickness reduces. However, if the thickness of the grouted soil layer rises threefold, the optimal thickness reduced by 17% and the optimal Young’s modulus increases by 30%. Thus, the optimal values of the Young’s modulus of the concrete shell is more sensitive to a change in the thickness of the of the grouted soil layer. Fig. 9 demonstrates effect of the lateral pressure P on the optimal parameters of the concrete shell. The lateral pressures correspond to the depth of 140, 190, 240 m. It can be seen that the optimal Young’s modulus decreases almost linearly with a rise in the lateral pressure. On the contrary, the optimal thickness increases sharply. At the depth