# Impact of Evaluation of Freeze-Thaw Cycles on Collapse Zone at Entrance and Exit of Loess Tunnel
## 4 Results of Freeze-Thaw Cycles on Strength Degradation of Loess  
Several freeze-thaw tests were carried out indoors on loess collected from Zichang County with the dry densities (1.60 g/cm\({}^{3}\)). The loess samples had three different initial water contents (16%, 20%, and 24%). During the tests, the freezing temperature and thawing temperature were set to -20 \({}^{\circ}\)C and 20 \({}^{\circ}\)C (Figure 11), respectively; the freeze-thaw time  
Figure 10: Collapse development predicted by the visual analysis program.  
Figure 9: Program interface of the visual analysis program.  
was set to 8 h; the number of freeze-thaw cycles were set to 0, 2, 4, 6, and 8. After the freeze-thaw cycles, the consolidated undrained (CU) test was performed immediately (Figure 12). Table 1 reported the test results.  
Figure 11: The whole process of preparation of soil samples.  
Figure 12: The consolidated undrained (CU) test under different freeze–thaw conditions: (**a**) Install; (**b**) Concretion; (**c**) Shear.  
The cohesion of the loess declined with the growing number of freeze-thaw cycles, and the declining trend slowed down until reaching a stable level, as shown in Figure 13. Based on the test data, the cohesion of the loess was degraded by 34.48%, 31.81%, and 31.54% under freeze-thaw cycle conditions of 8 times, with different initial water contents, respectively. The results reveal the degradation impact of freeze-thaw cycles on loess cohesion.  
The internal friction angle of the loess decreased with the growing number of freeze-thaw cycles, but at a very slow rate, as shown in Figure 14. Based on the test data, the internal friction angle of the loess was degraded by 15.52%, 9.7%, and 14.83% under freeze-thaw cycles conditions of 8 times, with different initial water contents, respectively. The results reveal the degradation effect of freeze-thaw cycles on the internal friction angle of loess. Any change of the angle would cause a shift to the maximum shear surface in the slip line field of the soil mass.  
With the increase of freeze-thaw cycle times, the cohesion and the internal friction angle of the loess strength decreased gradually, and this experimental phenomenon of loess strength attenuation is consistent with the analysis by [PERSON] et al. (2015), but it is worth noting that the attenuation of cohesion was significantly greater than that of the internal friction angle.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Strength** \\ **Indices** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Dry Density** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Water** \\ **Content\%** \\ \end{tabular} } & \multicolumn{5}{c}{**Number of Freeze–Thaw Cycles**} \\ \cline{5-8}  & & & **0** & **2** & **4** & **6** & **8** \\ \hline \multirow{3}{*}{c/kPa} & & 16 & 78.56 & 59.45 & 56.45 & 52.33 & 51.47 \\  & & 20 & 61.24 & 47.64 & 42.87 & 42.26 & 41.76 \\  & & 24 & 42.16 & 35.68 & 30.29 & 29.34 & 28.86 \\ \hline \multirow{3}{*}{\(\varphi/^{\circ}\)} & & 16 & 29.12 & 27.89 & 27.13 & 26.96 & 26.77 \\  & & 20 & 28.78 & 26.84 & 26.24 & 26.12 & 25.98 \\  & & 24 & 28.33 & 26.79 & 25.36 & 24.37 & 24.13 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Loess strength parameters under different freeze–thaw conditions.  
Figure 13: Trend of loess cohesion after freeze–thaw cycles.