## 2 Creep Tests of AS
### Results and Analysis  
#### 2.3.1 Strain-Time Curves and Creep Characteristic Curves of AS  
The strain-time curves of AS samples under different confining pressures were obtained by multi-stage loading tests. According to the principle of the multi-stage loading test, the strain-time curves for each loading stage could be obtained from the strain-time curves. The influence of confining pressures on the strain-time curves and strain-time curves for each loading stage of AS samples is shown in Figure 3. The following conclusions can be drawn from Figure 3. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{_C_ **(Mpa)**} & \multirow{2}{*}{\(\sigma_{c}\) **(MPa)**} & \multicolumn{5}{c}{\(\sigma_{i}\) **(MPa)**} \\ \cline{3-6}  & & \(\sigma_{\text{I}}\)/\(\delta\) & \(\sigma_{\text{II}}\)/\(\delta\) & \(\sigma_{\text{III}}\)/\(\delta\) & \(\sigma_{\text{IV}}\)/\(\delta\) & \(\sigma_{\text{V}}\)/\(\delta\) \\ \hline
3 & 42.5 & 23.5/55.29\% & 26.9/63.29\% & 30.3/71.29\% & 33.7/79.29\% & 37.1/87.29\% \\
6 & 47.35 & 26.4/55.76\% & 30.7/64.84\% & 35/73.92\% & 39.3/83.00\% & 43.6/92.08\% \\
9 & 52.75 & 30.3/57.44\% & 34.4/65.21\% & 38.5/72.99\% & 42.6/80.76\% & 46.7/88.53\% \\
12 & 57.37 & 33.6/58.57\% & 37.7/65.71\% & 41.8/72.86\% & 45.9/80.01\% & 50.0/87.15\% \\
15 & 62.92 & 36.9/58.65\% & 40.2/63.89\% & 43.5/69.14\% & 46.8/74.38\% & 50.1/79.62\% \\
18 & 67.3 & 39.6/58.84\% & 43.9/65.23\% & 48.2/71.62\% & 52.5/78.01\% & 56.8/84.40\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Multi-stage loading for creep tests of AS. Figure 3: Strain-time curves and strain-time curves for each stage of AS samples under various confining pressures: (**a**) 3 MPa, (**b**) 6 MPa, (**c**) 9 MPa, (**d**) 12 MPa, (**e**) 15 MPa, and (**f**) 18 MPa. 1. Regardless of the confining pressure, the deformation of AS samples at the initial loading stage increased with time, although at a decelerating rate. This stage is known as the primary creep stage. With continuous loading, the strain of the AS samples exhibited a linear response with time, and this stage is known as the secondary creep stage. At the final loading stage, which is known as the tertiary stage, the strain increased exponentially with time until the failure of samples. All AS samples exhibited three complete creep stages. 2. For creep tests with the same confining pressure, a certain amount of instantaneous deformation was observed when the stress loading at each stage was applied. Moreover, the deformation magnitude increased with increasing stress level. Instantaneous strain was the main component of the total strain. 3. With increasing confining pressure, the total instantaneous strain increased gradually. For example, when the confining pressure was increased from 3 MPa to 6 MPa, 9 MPa, 12 MPa, 15 MPa, and 18 MPa, the ratios of instantaneous strain to total strain were 61.2%, 63.1%, 65.2%, 67.3%, 70.2%, and 73.5%, respectively. 4. With increasing confining pressure, the failure load at the tertiary creep stage increased gradually. However, the failure load from the creep tests was less than the corresponding failure load from the conventional triaxial compressive tests. In summary, Figure 3 shows that all AS samples exhibited four complete creep stages, namely, instantaneous deformation stage, primary  
is provided as an illustration, and similar results could be observed at other loading stages. As shown, the creep deformation rates of AS samples under various confining pressures followed a decreasing-stable-increasing pattern. Detailed conclusions are drawn from Figure 5 as follows:  
1. Based on different confining pressures, the deformation rates of AS samples showed a fast decrease at the beginning. The deformation rate became stable within 7 to 9 h.
2. With increasing confining pressure, the average deformation rates in the stable stage were similar. However, evident differences were observed in the duration of the stable stage, which decreased gradually with increasing confining pressure.