PSI - Issue 32

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A. Kostina et al. / Procedia Structural Integrity 32 (2021) 101–108 A. Kostina/ Structural Integrity Procedia 00 (2021) 000 – 000

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Fig. 7. Horizontal displacements (m) in sand (a) at 4 th day after shutdown of freezing wells in case of soil freezing up to the contour of the shaft; (b) at 4 th day after shutdown of freezing wells in case of soil freezing up to the project thickness; (c) at 85 th day after shutdown of freezing wells in case of soil freezing up to the contour of the shaft; (d) at 24 th day after shutdown of freezing wells in case of soil freezing up to the project thickness. 4. Conclusions The work investigates safety of shaft sinking on the second stage of artificial ground freezing when freezing columns are turned off for drilling and blasting operations. Coupled thermo-hydro-mechanical model of soil freezing/thawing was applied for this purpose. The main equations of the model include mass balance equation, equilibrium equation and energy balance equation. Description of interaction between water migration and stress strain evolution is based on theory of poromechanics proposed by Coussy and effective stress concept. Numerical simulation was carried out for two soil stratums (silt and sand) and two initial thicknesses of frozen wall. The first thickness corresponded to the case when soil had been frozen up to the mine shaft contour. The second thickness of the wall corresponded to the project documentation. Results of numerical simulations have shown that soil moves into the mine shaft. Maximum values of stress near the unfixed section of the frozen wall in sand stratum are higher than in silt stratum. Maximum value of horizontal displacements for silt stratum at 4 th day of the thawing was obtained for the first thickness of the wall while for sand stratum this value was obtained for the second thickness. For silt stratum maximum displacement does not exceed critical value even for shutdown of the freezing wells for a period of 200 days. Deformation of the sand stratum has shown that loss of bearing capacity occurs at 85 th day of thawing for the first thickness and at 24 th day for the second thickness. This effect can be explained by significant thawing of frozen wall. Acknowledgements This research was supported by Russian Science Foundation (Grant No. 17-11-01204). References [1] Andersland, O.B., Ladanyi, B., 2013. An Introduction to Frozen Ground Engineering. Chapman and Hall, New York. [2] Levin, L., Golovatyi, I., Zaitsev, A., Pugin, A., Semin, M., 2021. Thermal monitoring of frozen wall thawing after artificial ground freezing: case study of Petrikov potash mine. Tunnelling and Underground Space Technology 107, 103685. https://doi.org/10.1016/j.tust.2020.103685. [3] Tsytovich, N.A., 1975. Mechanics of Frozen Soils. McGraw-Hill, New York. [4] Vyalov, S.S., 1986. Rheological Fundamentals of Soil Mechanics. Elsevier, Amsterdam, the Netherlands. [5] Lai, Y., Xu, X., Dong, Y., Li, S., 2013. Present situation and prospect of mechanical research on frozen soils in China. Cold Regions Science and Technology 87, 6-18. https://doi.org/10.1016/j.coldregions.2012.12.001. [6] Zhou, Z., Ma, W., Zhang, S., Du, H., Mu, Y., Li, G., 2016. Multiaxial creep of frozen loess. Mechanics of Materials 95, 172-191. https://doi.org/10.1016/j.mechmat.2015.11.020. [7] Zhelnin, M., Kostina, A., Plekhov, O., Panteleev, I., Levin, L., 2019. Numerical analysis of application limits of Vyalov’s formula fo r an ice soil thickness. Frattura ed Integrita Strutturale 13, 156-166. https://doi.org/10.3221/IGF-ESIS.49.17.