## 5 Conclusions  
In this paper, a series of triaxial compression tests covering a wide range of strain rates from \(10^{-6}\) to \(10^{-2}\) s\({}^{-1}\) were systematically conducted. The values of characteristic stresses and the ratios of macro-fracture characteristics with different strain rates and confining pressures were analyzed. The dynamic strength criterion within the strain rate were established. More importantly, the causes of strain rate effect discrepancies between \(\sigma_{\rm ci}\) and \(\sigma_{\rm cd}\) or \(\sigma_{\rm p}\) were discussed, and the mechanism underlying confining pressure sensitivity of strain rate effects on \(\sigma_{\rm cd}\) or \(\sigma_{\rm p}\) was proposed. The main conclusions can be summarized as follows:  
1. Under varying confining pressures, characteristic stresses of granite exhibit positive correlations with the logarithm of strain rate and confining pressure. Specifically, \(\sigma_{\rm cd}\) and \(\sigma_{\rm p}\) demonstrate significant linear positive correlations with the strain rate logarithm, while \(\sigma_{\rm ci}\) shows a relatively weaker correlation. 2. Under triaxial quasi-static loading conditions, the value of \(\sigma_{\rm ci}/\sigma_{\rm p}\) ranges from 0.41 to 0.56, and the value of \(\sigma_{\rm cd}/\sigma_{\rm p}\) ranges from 0.75 to 0.84. Linear regression analysis demonstrates strong linear correlations between \(\sigma_{\rm ci}/\sigma_{\rm p}\) and \(\sigma_{\rm cd}/\sigma_{\rm p}\), expressed as \(\sigma_{\rm ci}=0.58\sigma_{\rm p}\) and \(\sigma_{\rm cd}=0.85\sigma_{\rm p}\). 3. Macroscopic fracture patterns of granite are controlled by the confining pressure and strain rate: Y-shaped shear fractures predominantly form under low confining pressures and strain rates. With increasing confining pressure and strain rate, fracture patterns progressively transition to X-shaped shear-dominated failures. 4. The strain rate-induced enhancement of dynamic compressive strength primarily originates from the rate-strengthening effect on cohesion, while the internal friction angle remains stable across varying strain rates. 5. The disparity in microcrack activity intensity during different deformation stages of rocks leads to the CSDIF of \(\sigma_{\rm ci}\) being lower than those of \(\sigma_{\rm cd}\) and \(\sigma_{\rm p}\). 6. The CSDIF of \(\sigma_{\rm cd}\) and \(\sigma_{\rm p}\) decreases with elevated confining pressures. This differential behavior is explained by confinement-enhanced shear fracturing dominance during crack propagation stages combined with a lower strain rate sensitivity of shear versus tensile fracture toughness. Figure 19: DIF of granite specimens under tensile and compressive loading conditions [19; 42; 43; 44; 45]. (TDIF—tensile dynamic intensity factor; CDIF—compressive dynamic intensity factor; DTS—direct tensile strength; TBTS—three-point bending tensile strength; BSTS—Brazilian split tensile strength; UCS—uniaxial compressive strength; TCS—triaxial compressive strength; CP—confining pressure). **Author Contributions:** Conceptualization, L.L. and S.W. ; Methodology, J.O. ; Software, W.Y. ; Investigation, L.L. ; Data curation, L.L. and W.Y. ; Writing--original draft, L.L. ; Writing--review & editing, L.L. and J.O. ; Visualization, S.W. ; Supervision, J.O. and S.W. ; Funding acquisition, J.O. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by [Scientific research program of China Yangtze Power Co., Ltd.] grant number [1524020050] and The APC was funded by [Scientific research program of China Yangtze Power Co., Ltd.: 1524020050]. **Insitutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.