# Experimental Study on the Pre-Peak Mechanical and Seepage Characteristics of Granite
## 4 Conclusions  
In this paper, triaxial compression tests and stress-permeability coupling tests were carried out on granite to analyze the evolution laws of characteristic thresholds, deformation, and permeability in the progressive failure process of granite under different confining pressures, in addition to calculating the effective stresses of the granite under different confining pressures and carrying out the evaluation of the sensitivity of the effective stresses. The main conclusions are as follows:  
1. The closure threshold, crack initiation threshold, damage threshold, and peak strength divide the evolution process of granite's pre-peak mechanical characteristics into a crack closure stage, linear elasticity stage, stable crack expansion stage, and unstable crack expansion stage. The confining pressure is positively correlated with the closure threshold, peak strength, and damage threshold.
2. In the evolution of the pre-peak permeability characteristics of granite, when the confining pressure is certain, the permeability decreases and then increases with the increase in axial stress, which is more in line with the four phases of the crack change in the progressive damage analysis. The confining pressure is negatively correlated with the peak permeability of granite. Especially, the peak permeability at a high confining pressure differs by one order of magnitude from the peak permeability at a medium confining pressure.  
Figure 11: Effective stress and effective stress sensitivity coefficient under different confining pressures.  
3. The polynomial model can better fit the relationship between effective stress and the permeability of granite. The effective stress sensitivity coefficients of granite are differently reflected at different confining pressures. At a medium confining pressure, the permeability of granite is more affected by the effective stress, while at low and high confining pressures, the effective stress has less effect on the permeability of granite. At medium and high confining pressures, with the increase in the effective stress, the stress sensitivity of the permeability of granite gradually tends to diminish, while at a low confining pressure, the trend is to increase.  
Based on previous research, the closure threshold, crack initiation threshold, and damage threshold of granite were determined with the axial strain difference, crack volumetric strain curve, and volumetric strain curve, and the evolution law of progressive failure of granite under different confining pressures was obtained. The evolution law of the permeability of granite with stress under different confining pressures was obtained by combining progressive failure analysis with stress-seepage coupling analysis. The stress sensitivity analysis of granite permeability under different confining pressures was carried out, and the relationship between effective stress and permeability and the stress sensitivity coefficient of granite permeability under constant confining pressure was obtained.  
The bedrock of submarine deposits is a complex hydrogeological environment. There are some shortcomings in the design of this experiment, and the hydrological environment of its occurrence was not fully reflected. The stress-seepage coupling direction of granite after corrosion can be further explored.  
Conceptualization, Q.Z.; Methodology, X.Z., W.L. and Q.Z.; Software, X.Z. and X.C.; Validation, X.Z.; Data curation, Q.Z.; Writing--original draft, X.Z., W.L. and X.C.; Writing--review & editing, Q.Z.; Visualization, W.L. All authors have read and agreed to the published version of the manuscript.  
The authors are grateful for the financial support from the National Natural Science Foundation of China (grant no. 52004332).  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors declare no conflict of interest.