PSI - Issue 17

M. Zhelnin et al. / Procedia Structural Integrity 17 (2019) 316–323 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

317

2

technique is widely applied in geotechnical engineering to shaft sinking under complex geological and hydrological conditions. The aim of AGF is formation of a temporary ice-soil retaining structure around the intended excavation. As freezing of ground leads to reduce of its permeability and improve the strength and stiffness properties, the ice soil wall eliminates groundwater filtration into the excavation and prevent squeezing of the excavation wall by rock pressure. To create an ice-soil wall, series of freezing wells are drilled along circumference of a mine shaft that is planned to be build. Due to circulation of a liquid refrigerant through freezing pipes that are installed in the wells, heat extracts from the rock mass and temperature of ground around the wells decreases. Freezing of water contained in pores of soil involves a complex interaction of thermal, hydrodynamic and mechanical processes. Frost heave of a rock-mass is a key phenomenon for geotechnical engineering that is induced by this interaction. Conversation of pore water into ice causes volume expansion of the pore spaces that leads to occurrence of frost-heaving pressure that has a significant influence on geotechnical structures (Sres et al. (2006)). In Wang and Zhou (2018) a review of studies related to an influence of frost-heaving pressure on geotechnical structures is proposed. It is noted that frost-heaving pressure is determined by a value of ice saturation and a freezing rate. In Han et al. (2015), Gao et al. (2012), Liu et al. (2018) stress and strain induced by frost heave of soils surrounding of tunnel constructions are considered. On the basis of in situ monitoring data and numerical simulation in Han et al. (2015) has been shown that frost-heaving pressure induced by AGF leads to change of the rock pressure distribution in neighborhood of the tunnel excavation. In Gai et al. (2012) and Lie et al. (2018) analytical elasto-plastic solutions for stress and strain in frozen soils surrounding a tunnel have been obtained. It has been shown that frost-heaving pressure gives rise to expansion of plastic zone in the soils. Studies of strength of frozen soils are presented in Tsytovich (1975), Liu et al. (2019), Lai Y. et al. (2013), Fish (1991), Qi and Ma (2007). In Tsytovich (1975), Liu et al. (2019) it is noted that a decrease of temperature and unfrozen water content leads to an increase of strength of frozen soils. In Lai Y. et al. (2013) it is discussed various laws for description strength on temperature. Confining pressure is another factor that effects on strength. It is noted that for up to a certain critical value of confining pressure strength of frozen soil increases. In this case it can be described by Mohr – Coulomb criterion and Drucker – Prager criterion (Tsytovich (1975), Liu et al. (2019), Lai Y. et al. (2013)). High values of confining pressure leads to pressure melting and crushing of ice in soil pores. As a result, the strength of the frozen soil reduces. For this case modifications of the criteria have been proposed (Fish (1991), Qi and Ma (2007)). In recent times to describe freezing process of soil thermo-hydro-mechanical models are developed Kruschwitz and Bluhm (2005), Zhou and Meschke (2013), Liu et al. (2018). The models allow one to take into account interaction between mechanical behavior of soil, temperature and water filtration during freezing process. In Kruschwitz and Bluhm (2005), Zhou and Meschke (2013) it is supposed that frost heave causes only elastic deformation of soil. In Liu et al. (2018) constitutive relations for elasto-plastic deformation of soil are developed on the basis of thermo poromechanics and the theory of hardening plasticity. The present work is devoted to a numerical simulation of stress-strain state of soils around of freezing wells during a vertical mine shaft construction with an application of the AGF method. The numerical simulation is performed on the basis of a thermo-hydro-mechanical model Panteleev et al. (2017). Constitutive relations are derived within framework of thermo-poromechanics with consideration of the phase transition. Conducted in Panteleev et al. (2017) a comparison of temperature distributions obtained by numerical simulation of AGF of rock mass at Starobinsky potash deposit with temperature measurements shows good agreement between data. In the present work determination of mechanical behavior of soils surrounding freezing wells is carried out for two cases. In the first case an influence of frost heave and unloading induced by shaft sinking on stress distribution in large domain including the wellbores is studied. In the simulation the rock mass is supposed to be multi-layered elastic material that undergoes small deformation. In the second case an analysis of stress and strain distributions in a neighborhood of the one wellbore is conducted. In the case plastic deformation of soil is considered. To describe plastic strain Drucker-Prager criterion is used.