PSI - Issue 17

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

320

5

Table 2. Mechanical properties of soils Soil K, Pa G, Pa

C , Pa

φ  73 14 11

s  , 1/K

B 

Sandstone

5.91·10 9 8.08·10 9 2.82·10 9 2.33·10 9 1.92·10 8 1.54·10 8

10.2·10 6 4.08·10 6 2.72·10 6

2.14·10 -5

4.51·10 -1 5.07·10 -1 5.72·10 -1

Sand Clay

5·10 -6

0

b

a

Fig. 1. Distributions of the mechanical pressure (a) and Mises stress (b) in the first computational domain at t = 200day. White lines denote the phase transition interface.

presented at t = 200 day after the artificial freezing process has been started. From Fig. 1(a) it can be seen that freezing of soils causes an increase of the pressure. At that the pressure rises in horizontal directions from the excavation boundary to the wells, after that it decreases. The distribution of Mises stress is qualitative different. From the excavation boundary the stress drops to a certain value after that it begins to rise right up down to the wells boundaries. In horizontal directions from the wells to the external boundary the stress decreases. Thus it can be concluded that AGF leads to an increase of the mechanical pressure and Mises stress. The unloading induced by the shaft sinking also causes a rise of the pressure, but it leads to a reduce of Mises stress in frozen soils. In neighborhoods of the wellbores a rise of the pressure and the stress is observed. In Fig. 2(a) distributions of the mechanical pressure and the Mises stress along the well boundary are shown at t = 200 day. It can be seen that at interfaces of soil stratums the pressure and the stress abrupt rise. The maximum value of the pressure is at the interface of the clay and sand stratums. In the sandstone stratum a mean value of the pressure is higher than other stratums. The stress also attains the maximum value at this interface. In Fig. 2(b) the phase transition boundary and vector fields of displacement are presented at t = 200 day. It can be seen that soil stratums are subsided to down, as it is supposed that the vertical displacement on the top boundary of the sandstone stratum is restricted by the upper soil stratum with higher stiffness. The maximal displacement is observed in the clay stratum.