PSI - Issue 13

Kostina A. et al. / Procedia Structural Integrity 13 (2018) 1273–1278 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Thus the ice-soil wall is an important geotechnical construction, strength and reliability of that determine safety of the shaft sinking. Despite the long-term experience of using the artificial freezing technique, numerous accidents and technological problems arise under the excavation of mine shafts at great depths. To prevent emergencies and guarantee the fulfilment of designed characteristics of mine shafts it is required conduction of through studies of mechanical behavior of the ice-soil wall (Panteleev et al. (2017)). Frozen soils, because of the presence in them of ice and unfrozen water, possess clearly defined rheological properties such as development imperceptibly slow deformations (creep) and losing strength during a prolonged load action. In (Vyalov (1986), Razbegin et al. (1996), Arenson et al. (2007), Qi et al. (2013), Lai et al. (2013)) extensive reviews of experimental and theoretical studies related to frozen soils are presented. The Vyalov’s constitutive relations (Vyalov et al. (1962), Vyalov et al. (1979), Vyalov (1986)) give one of the basic mechanical model for describing rheological properties of frozen soils. According to the relations creep strain is described by the Norton-Bailey power law (Ottosen and Ristinmaa (2005)) in that a modulus depends on time and temperature and it is assumed that volume deformation under creep can be neglected. Experimental studies confirm that the theory allows one to describe of the creep in wide range of temperatures. In particular, in (Vyalov et al. (1962), Klein and Jessberger (1979), Eckardt (1982), Vyalov (1986)) an analysis of the experimental data of creep of various type of frozen soils in uniaxial compression and tensile tests has been conducted based on the theory. In (Vyalov et al. (1979)) theory has been justified by experimental results of uniaxial and triaxial compression tests performed for frozen dusty loam and two types of clay. Based on the theory the Vyalov’s formula for estimating of an optimal thickness of an ice -soil wall for that it can resist to given rock pressure has been derived (Vyalov et al. (1979)). This formula is widely used by engineers for design the ice-soil wall and determination of optimal parameters for the artificial ground freezing (Andersland and Ladanyi (2013)). However, the formula has been obtained analytically with strong assumptions, which could differ from real conditions under shaft construction. In recent times for prediction of a mechanical behavior of soils and a mine shaft during the excavation process and the installation of the shaft support applied numerical simulation. In (Judeel et al. (2012)) an elastic behavior of a cast iron tubbing lining during mine shaft construction has been researched. In (Fabich et al. (2015)) displacement of a shaft wall before installation of the shaft lining has been estimated with considering an ideal elasto-plastic behavior of soil and the Hoek-Brown strength criterion. In (Oreste et al. (2016), Spagnoli et al. (2017)) an approach for estimating radial loads on a vertical shaft lining and radial soil displacement during the excavation have been developed on the basis of the Mohr-Coulomb strength criterion. In (Schwamb and Soga (2015)) an analysis of monitoring data obtained at several shaft excavation levels has been numerically performed with using the Mohr-Coulomb and the Hoek-Brown failure criteria. In (Jia et al. (2008)) a numerical modelling of hydromechanical response of argillite during a shaft sinking have been carried out taking into account plastic and creep deformations. This work is devoted to verification of the Vyalov’s formula at various depth of a shaft sinking by finite element numerical modelling of a vertical mine shaft with the unsupported wall. The creep behavior of frozen soil was described by using the Vyalov’s constitutive relations. The mechanical properties were determined from experimental data for Callovian sandy loam as one of the most dangerous soil layer for a sinking. The rock pressure was estimated by applying a standard structural design approach (Farazi and Quamruzzaman (2013)) based on the Rankine’s theory (Terzaghi et al. (1996)). According to (Vyalov et al. (1979)) a vertical mine shaft sinking by the artificial ground freezing technique is performed by the following way. An ice-soil retaining structure represented as an ice-soil cylinder is formed around the building mine shaft. As the shaft is sunk the outer surface of the cylinder is loaded by rock pressure P . However, the shaft sinking is carried out incrementally together with installation of the shaft lining that is supported the shaft wall. Therefore, a relatively small height h of the inner surface is unsupported. This part of the retaining structure is deformed under an effect of the pressure P within some time period pr t that is required for building of the lining. It is known because of creep of frozen soils even if plastic deformation of the ice-soil retaining structure does not occur, creep deformation of the cylinder wall could reach significant values. As a result, freezing columns could fail and the installation of the shaft lining could be complicated. Thus, the thickness of the cylinder wall is 2. Theoretical model