PSI - Issue 32

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 illustrates horizontal displacements in sand. It can be seen that for both thicknesses maximum displacements do not exceed critical value and equal to 3.4 mm for the first case (Fig. 7 (a)) and 3.6 mm for the second case (Fig. 7 (b)). Maximum displacements in silt stratum for this period of time are higher in 2.9 times for the first thickness and in 2.8 times for the second thickness. This can be explained by the fact that frozen sand has higher elastic properties and, therefore, is more rigid material than frozen silt. Further calculations have shown that loss of bearing capacity will occur on 85 th day (Fig. 7 (c)) when initial thickness coincides with the shaft contour and on 24 th day (Fig. 7 (d)) when initial thickness is equal to project documentation. Loss of bearing capacity is explained by considerable thawing of the soil which increases its compliance related to lower values of elastic properties for unfrozen ground in comparison with frozen.

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(b)

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Fig. 6. Horizontal displacements (m) in silt (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 200 th day after shutdown of freezing wells in case of soil freezing up to the contour of the shaft; (d) at 200 th day after shutdown of freezing wells in case of soil freezing up to the project thickness.

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