## 3 Results and Discussion  
### Loading Creep Curve of Unloaded Specim  
The loading creep curve mainly reflects the rock strain development process with the passing of time and the increase in stress level. Figure 5 shows the loading creep curves of unloaded samples under different conditions. In Figure 5, it can be seen that the overall trends of the creep test curves of the two groups with different values of confining pressure are the same, with the increase in stress level corresponding to the gradual changes in the creep stage: deceleration creep, stable creep, and accelerated creep are the three typical creep stages. Under the initial confining pressure of 15 MPa, the creep behaviour of specimen R15-0 of the normal temperature test group is not obvious, and the creep curve reflects that the strain of the specimen before the stress reaches the long-term strength is mainly the transient strain generated when the load is applied. The creep deformation accounts for a very small amount, and there is no obvious change in the axial and lateral directions of the specimen under the same creep time at different stress levels. Sample R15-7 is similar to sample R15-0 in terms of their creep curves at 7 days of freezing, and the creep deformation is not obvious before in the damage stage. In contrast, sample R15-14 is significantly different at 14 days of freezing, and the lateral expansion phenomenon is obvious at the 60% stress level. The lateral creep curve develops with a certain slope at this stage, and the strain also increases significantly. The creep curves of the three samples under the initial confining pressure of 21 MPa are significantly different. The creep damage of specimen R21-0 of the normal temperature test group occurs at a load level of 70%: the damage occurs suddenly and the creep curve is smooth before the damage stage. Test group R21-7 underwent damage during loading at the 70% load level, exhibiting significant lateral deformation before damage. For test group R21-14, at a load level of 60% after 1.5 h of creep damage, the creep curve exhibits a significantly accelerated creep phase. Comparing the initial confining pressures of the 15 MPa and 21 MPa test groups, the deformation of specimens with an initial confining pressure of 21 MPa is greater than that of specimens with an initial confining pressure of 15 MPa in the same freezing period before specimen damage occurs. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Specimen Number** & **Initial Confining Pressure** & **Creep Confining Pressure** & **Freeze Period** \\  & **/MPa** & **/MPa** & **/Day** \\ \hline R15-0 & & & 0 \\ R15-7 & 15 & 6.75 & 7 \\ R15-14 & & & 14 \\ \hline R21-0 & & & 0 \\ R21-7 & 21 & 12 & 7 \\ R21-14 & & & 14 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental grouping. Summarizing the above trends, firstly, the effect of freeze-thaw time on the deterioration of rock samples is not obvious when the initial confining pressure is relatively low. The reasons for this are that the relatively low initial confining pressure characterizes the relatively low unloading level and the structural damage caused by unloading is small; however, the degree of damage to the rock by a single freeze-thawing action depends on the number and size of cracks within the rock, and then the relatively low initial confining pressure corresponds to a smaller structural damage to the rock, resulting in weaker freeze-thaw deterioration. This also reflects that the unloading process is the main cause of structural damage in rock compared with freeze-thaw action, which is the main factor affecting the safety and stability of rock works. Secondly, the lateral creep behavior of the rock sample is more obvious than the axial when the initial confining pressure is the same.