## 5 Conclusions  
This paper provides a reference foundation for the safety production and disaster prevention of underground space engineering. If we can determine the axial stress of the rock surrounding the tunnels in environments of temperature and groundwater coupling, we can more quickly judge whether safety measures should be taken to ensure the safe operation of underground projects. However, because the rock samples used in these tests  
Figure 14: Relationship between absorbed energy ratio and average particle size.  
Figure 13: Variation of specimen energy with axial pressure.  
were relatively limited, only the mechanical properties of local sandstone were studied. Moreover, the relevant test design was not perfect. As a result, the results obtained could characterize the properties of sandstone only under specific conditions, and the research results can be applied only under specific local geological conditions. In the future, when the experimental design is perfected, it will be possible to carry out tests on other rocks under the same conditions presented in this paper.  
This paper presents the following main conclusions drawn from impact compression tests on temperature-water-coupled sandstones carried out under different axial pressure loadings using a dynamic-static combined SHPB test setup:  
1. The mineral composition of the sandstone samples was mainly quartz, kaolinite, and illite. The mass, volume, and density of the sandstone samples increased by 0.57%, 0.37%, and 0.20%, respectively, after temperature-water coupling.
2. Axial pressure loading reduced the bearing capacity of temperature-water-coupled sandstone specimens. Additionally, the dynamic compressive strength of the specimens was distributed as a linear function showing a decrease with an increase in axial pressure and a quadratic positive correlation between the dynamic peak strains.
3. As the axial pressure increased, the internal structure of the temperature-water-coupled sandstone specimen became continuously damaged, resulting in the specimen's dynamic Young's modulus showing a quadratic downward trend. Moreover, the average strain rate showed an exponential increase, with a more pronounced strain rate effect.
4. The temperature-water-coupled sandstone specimen's absorption energy increased continuously with axial pressure. Additionally, the average particle size of the specimen is negatively correlated with the axial pressure as a linear function and quadratically decreases with the absorbed energy of the specimen.  
Conceptualization, S.S.; data curation, J.H.; funding acquisition, Q.P.; methodology, Q.P.; software, J.H.; supervision, Y.X., S.W., X.L., and S.S.; validation, X.L.; visualization, Y.X. and S.W.; writing--original draft, Q.P. and J.H. All authors have read and agreed to the published version of the manuscript.  
National Natural Science Foundation of China: no. 52074005 and no. 52074006; The Anhui Natural Science Foundation: no. 1808085 ME134; The Anhui Postdoctoral Science Foundation: no. 2015B058.  
Not applicable.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
Thanks to the State Key Laboratory of Mine Response and Disaster Anhui University of Science and Technology for providing the experimental conditions.  
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.