## 6 Conclusions  
This study conducted lab tests, a parameter inversion method, and numerical simulations on a water diversion project in Xinjiang to determine the creep characteristic models of mudstone collected from the surrounding rocks as well as the construction timing and safety of lining. The following conclusions can be drawn:  
1. The strain of the mudstone of the supporting work under loading at each stage can be divided into transient strain and creep strain. The mudstone exhibited decay creep under a low deviatoric stress, decelerated creep and isokinetic creep under an intermediate deviatoric stress, and steady creep under a high deviatoric stress. The Burgers model was adopted as the creep constitutive model for the mudstone.
2. The Burgers-Mohr model that considers the yield characteristics of mudstone was used to model the rock mass. To establish the GA-BP neural network inversion model, 100 orthogonal tests were performed using random creep parameters. The long-term  
Figure 17: Surrounding rock deformation characteristics at the earliest lining time: (**a**) XZ43+090, (**b**) XZ67+070.  
deformation data of the arch and sidewall of the tunnel were monitored in situ, and the creep parameters of the mudstone rock mass of XZ43+090 and XZ67+070 were obtained. The creep deformation of the surrounding rock was observed to be stable 300 days after the installation of the support, after which the creep effect decreased.
3. Based on the long-term creep deformation characteristics, the initial support, and the stress of the lining of the surrounding rocks, the optimal timing of lining for XZ43+090 and XZ67+070 was determined as 90-110 and 80-100 days after the support installation, respectively. The construction of the lining during these periods is ideal to meet the requirements for the deformation and deformation rate of the surrounding rocks to ensure the safety of the support and lining. The results of this study can serve as a reference for similar projects in China and worldwide.  
It is worth noting that the current research, limited by space and calculation time, specifically focuses on investigating the creep properties of surrounding rocks in a particular project in Xinjiang. However, the research and analysis methods employed possess universal applicability, allowing for their extension to the study of creep properties in surrounding rocks under various geological engineering conditions. Consequently, future research can entail conducting numerous studies on the creep behavior of surrounding rocks with different geological conditions, burial depths, and rock types. These studies can utilize machine learning methods for the analysis and synthesis of research findings, with the ultimate goal of summarizing the results into universally applicable laws governing the creep parameters of surrounding rocks.  
Conceptualization, J.P.; formal analysis, L.L. and X.W.; investigation, J.P. and Y.L.; resources, L.L., X.W. and Y.L.; data curation, J.P. and Y.L.; writing--original draft, J.P. and Y.L.; writing--review and editing, J.P., L.L. and Y.L.; supervision, L.L. and X.W.; project administration, J.P. and Y.L.; funding acquisition, L.L. All authors have read and agreed to the published version of the manuscript.  
This work was financially supported by grants from the National Natural Science Foundation of China, China (Grant No. 52179121, 51879284), the IWHR Research & Development Support Program, China (Grant No. GE0145B012021), and State Key Laboratory of Simulations and Regulation of Water Cycle in River Basin (Grant No. SKL2022 ZD05).  
Not applicable.  
All data, models, or code that support the findings of this study are available from the corresponding authors upon reasonable request.  
Author [PERSON] was employed by the company Construction and Management Branch of CSG Power Generation Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.