Issue 63

L. Levin et alii, Frattura ed Integrità Strutturale, 63 (2023) 1-12; DOI: 10.3221/IGF-ESIS.63.01

inhomogeneity of the FW temperature field, its geometric dimensions, and the strength properties of the soils, it was possible to calculate the time dependencies of the limiting value of the load on the FW using formula (8). The obtained time dependencies are shown in Fig. 8.

Figure 8: Time dependencies of the limiting value of the external lateral load that the FW can withstand Fig. 8 shows that, in general, for 12 months, for all the considered soil layers, the FW strength increased. Simultaneously, the limiting values of the external load according to formula (8) were quite large and after four months exceeded the actual external load. For sand, the external load was 0.17 MPa, for sandy clay, it was 1.36 MPa, and for clay, it was 1.54 MPa. These values were calculated as the sum of two components: the lithostatic pressure and the pressure of the water column at the level of the bottom of each considered soil layer. The limiting value of the external lateral load according to formula (12) was significantly lower, which was associated with the features of this formula and the physics included in it [25]. After only 6 months, this limiting value for the clay layer exceeded the actual external load that was calculated during the engineering and geological surveys and the development of the design documentation for the AGF (Fig. 8b). In general, according to both formulas, the selected operation mode of the freezing station provided a significant margin for the required thickness of the FW during the construction period of the shaft. This was because when choosing the operating mode of the freezing station, the mine specialists were guided by other criteria:  Maintaining the average temperature of the FW at a level of -8 to -10°C. It was for these temperatures that the design thicknesses of the FW were calculated.  Sufficient freezing of the soils at a depth of 140 m, where the seepage flow of the pore water was revealed [20]. In addition to this, the analysis of the dynamic change in the FW bearing capacity presented in this paper was conducted after the construction of the skip shaft in the AGF interval of 0 to185 m. Moreover, the analysis conducted in the present study will be useful primarily for mine shafts that will be built in the future. The data presented herein also did not account for the FW creep. The calculation of the required thickness of the FW according to the creep criterion is also mandatory in the design of the AGF [26, 27]. The calculated values of the FW thicknesses according to the creep condition for the relatively deep layers (sandy clay, clay) may be higher than the calculated values of the FW thicknesses according to the strength condition. his paper describes a method for analyzing the dynamically changing bearing capacity of an FW according to temperature monitoring data. In the first stage, according to the temperature readings in the CT boreholes, the temperature field was interpreted throughout the entire frozen soil volume, and the actual FW thicknesses were determined from the soil freezing isotherms. Furthermore, the resulting temperature field was used to calculate the inhomogeneous distribution of the physical-mechanical and strength properties of the FW and determine the limiting value T C ONCLUSION

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