# Experimental Study on Dynamic Mechanical Properties of Sandstone Under Different Damage Degrees
## 7 Conclusions  
This study conducts a series of dynamic mechanical performance experiments on rock specimens drilled with impact loads to analyze the effects of impact loads on rock damage properties under non-geostress conditions in open-pit mining and under various geostress conditions in the drilling process of underground mining and tunnel excavation. The experimental results are used to investigate the strength properties and energy consumption characteristics of damaged rocks under impact loads. Based on the analysis of data obtained from loading experiments on the rock specimens under dynamic loads, the primary findings are listed below.  
Firstly, the strain rate loaded by the SHPB apparatus is positively correlated with the magnitude of impact pressure when launching the spindle-shaped striker. During dynamic uniaxial testing, the compressive strength of the rock is significantly influenced by the strain rate, meaning that the uniaxial compressive strength of the rock rises as the strain rate increases.  
Secondly, the compressive strength of rock samples drilled with different impact loads in the dynamic uniaxial experiment is inversely related to the impact power during drilling; higher impact power results in lower compressive strength. The failure pattern of the rock after the dynamic uniaxial experiment is related to energy absorption, with greater energy absorption leading to smaller fragment sizes after failure. The intensity of dynamic loading and the degree of damage to the rock itself are the main factors affecting the energy absorption of rocks. The greater the values of these two factors, the more energy the rock absorbs.  
Lastly, in the triaxial dynamic experiment, the rock's compressive strength demonstrates both a strain rate effect and a confining pressure effect. In other words, an increase in strain rate leads to higher compressive strength, and similarly, an increase in confining stress results in higher compressive strength. Confining stress not only affects the compressive strength of the rock but also influences the deformation process and energy absorption during rock fracture. Therefore, during underground mining or tunnel excavation, efforts should be made to minimize the influence of confining stress on the drilling process.  
Figure 20: Failure pattern of sandstone in the triaxial dynamic compression experiment. (**a**) Failure pattern of rock samples drilled with high-impact load. (**b**) Failure pattern of rock samples drilled with non-impact load.  
**Author Contributions:** Conceptualization, Z.L., X.S. and W.W.; methodology, Z.L. and W.W.; formal analysis, Z.L.; data curation, X.S.; writing--original draft, Z.L.; writing--review and editing, Z.L. and X.S.; funding acquisition, X.S. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Project of the National Natural Science Foundation of China (Grant No. 52304227), the Natural Science Foundation of Hunan Province (Grant No. 2023 JJ40548), the Research Project of Education Department of Hunan Province (Grant No. 22B0426), and the Scientific and Technological Research Platform for Disaster Prevention and Control of Deep Coal Mining (Anhui University of Science and Technology) (NO. DPDCM2208).  
**Institutional Review Board Statement:** Not applicable.  
**Data Availability Statement:** The data used to support the findings of this study are included within the article.  
**Conflicts of Interest:** The authors declare no conflicts of interest.