## 4 Freeze-Thaw Test Results and Analysis
### Analysis of Peak Strength Deterioration after Freeze-Thaw and Reloading of Unloaded-Damaged Samples  
Uniaxial and triaxial reloading tests were conducted on the unloaded-damaged samples for a defined number of freeze-thaw cycles. From the above analysis, it can be seen that the degree of damage of the unloaded-damaged samples and the response to freeze-thaw deterioration are not related to the size of the initial confining pressure. Uniaxial reloading tests after freeze-thaw were carried out using the group A unloaded-damaged samples, and the test results are grouped and named group D. For the perimeter pressure value of the triaxial reload mechanics test, the confining pressure unloading target values (5.8 MPa, 8.4 MPa, and 12.5 MPa) for the preparation of the unloaded-damaged samples are selected  
Figure 10: Damage characteristics of the unloaded-damaged samples after freeze-thaw cycles as well as uniaxial and triaxial reloading. and called the unloading residual confining pressure values. The test results are shown in Table 2, and the strength damage rate \(\delta\) is:  
\[\delta=\frac{F_{0}-F_{n}}{F_{0}}\times 100\% \tag{4}\]  
where \(F_{0}\) is the peak uniaxial and triaxial reloading strength of the unloaded-damaged sample after 0 freeze-thaw cycles, and \(F_{n}\) is the peak uniaxial reload strength of the unloaded-damaged sample after \(n\) freeze-thaw cycles. From Figure 11, it can be seen that the trend in the uniaxial and triaxial reloading peak strength loss rate of the unloaded-damaged samples is more or less the same; that is, the strength loss rate increases gradually with the increase in the number of freeze-thaw cycles. The uniaxial reloading peak strength loss rate of the unloaded-damaged samples is higher than that of triaxial in the overall number of freeze-thaw cycles, and it is controlled by the size of the unloading residual confining pressure, which shows that the larger the value is, the smaller the strength loss rate. The main reason is that the freeze-thaw cycle is partially inhibited by the compression of the annular structure of the rock sample in the hydrostatic pressure loading stage in the triaxial reloading test after freeze-thawing of the unloaded-damaged samples. This weakens the freeze-thaw deterioration effect and leads to a reduction in the peak strength loss rate. The larger the enclosing pressure is, the more obvious the degree of inhibition. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Number of**} & \multicolumn{5}{c}{**Triaxial Reloading Test**} & \multicolumn{5}{c}{**Uniaxial Reloading Test**} \\ \cline{2-9}  & **Group A** & **Strength** & **Group B** & **Peak** & **Strength** & **Group C** & **Peak** & **Strength** \\
**Taw** & **Peak** & **Damage** & **Peak** & **Damage** & **Range** (\%) & **Strength** & **Range** (\%) & **Strength** \\
**Cycles** & **(MPa)** & **Rate (\%)** & **(MPa)** & **Rate (\%)** & **Rate (\%)** & **(MPa)** & **Rate (\%)** & **(MPa)** & **Rate (\%)** \\ \hline
0 & 110.66 & 0.000 & 125.41 & 0.000 & 145.79 & 0.000 & 37.20 & 0.000 \\
2 & 107.17 & 3.153 & 122.22 & 2.544 & 143.32 & 1.694 & 34.32 & 7.742 \\
4 & 105.29 & 4.853 & 120.51 & 3.907 & 142.35 & 2.359 & 33.70 & 9.409 \\
6 & 103.61 & 6.371 & 118.45 & 5.549 & 140.47 & 3.649 & 32.89 & 11.586 \\
8 & 100.10 & 9.452 & 116.08 & 7.439 & 137.60 & 5.618 & 31.33 & 15.779 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Unloaded-damaged samples uniaxial and triaxial reloading peak strength. Figure 11: Relationship between the number of freeze-thaw cycles and the peak strength damage rate. The rock body of the excavation and unloaded zone of a slope in cold regions is in a three-way stress state, and the freeze-thaw cycle erosion induced by the climatic environment of the site aggravates the damage deterioration of the excavation and unloaded rock body.