## 5 Conclusions  
In this study, the creep behaviors of AS were investigated both experimentally and numerically. Multi-stage creep tests were conducted on AS samples under different confining pressures (3, 6, 9, 12, 15, and 18 MPa). The creep characteristics of AS were analyzed. Based on the experimental results, a new nonlinear creep model was proposed. The nonlinear creep model was implemented in the FLAC3D software, and the procedure for the model parameter determination was presented. A comparison between the numerical and experimental results was also conducted for numerical modelling validation. Based on the above results, the following conclusions can be drawn:  
1. During the creep tests, the AS samples under various confining pressures exhibited four stages: instantaneous deformation, primary creep, secondary creep, and tertiary creep. With increasing confining pressure, the acceleration rate of the AS samples increased, and the creep failure strength gradually increased. However, due to the confining effect of confining pressure, the final volume gradually decreased. 2. The nonlinear creep model of AS was constructed by adding another element, the NVPB element, to the traditional Nishihara model. The three-dimensional form of the creep model was deduced to simulate the rock creep problem under the equal confining pressure of surrounding rock masses. The parameters of the creep model could be obtained by fitting the least squares method. 3. Based on the principle of finite difference, the finite difference form of the nonlinear creep model of AS was derived, and the model was embedded in the FLAC3D software. The numerical calculation model of AS was established. The creep behaviors of specimens under a confining pressure of 18 MPa were calculated and verified with experimental data. A good agreement was observed between the numerical and experimental results, indicating the feasibility of the creep model. 4. The creep and rupture process of rock is a process of damage accumulation essentially, which is not only related to the confining pressure, but also closely affiliated with factors such as loading rate and initial damage degree etc. In this paper, as the dominant factor in the engineering case, the confining pressure is used as a variable to carry out creep test research, which has certain limitations and will be supplemented in the future. Figure 12: (**a**) Three-dimensional creep numerical model of AS. (**b**) Comparisons between numerical results and experimental results. **Author Contributions:** Conceptualization, H.Z. and Q.C. ; methodology, H.Z. ; software, M.L., I.M.J. ; validation, W.Z., H.Z. and C.Q. ; formal analysis, H.Z. ; investigation, Y.Z. ; resources, W.Z. ; data curation, X.L. ; writing--original draft preparation, H.Z. ; writing--review and editing, W.Z. ; visualization, X.L. ; supervision, Q.C. ; project administration, Q.C. ; funding acquisition, W.Z. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the Independent Research Project of State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (SKLCRSM18X001). **Conflicts of Interest:** The authors declare no conflict of interest.