## 3 Experimental Results and Analysis
### Strength Characteristic Analysis  
When the shale is softened by water, aging deformation occurs, which leads to the accumulation of internal water, causing physical and chemical damage, and this leads to the spread, propagation, penetration, and collapse of initial defects in the shale rock mass. During the micro-deformation process, the chemical interaction between water and shale composition significantly affects its strength. By fitting the test data, the relationship between the triaxial compressive strength and water content of the shale rock under different confining pressures can be obtained. At the confining pressure of 60 MPa,  
\[\sigma=3.7071\;\mathrm{W}+42.7358, \tag{1}\]  
Formula: \(\sigma\) is the triaxial compressive strength (MPa) of shale; \(\mathrm{W}\) is the moisture content (%); the correlation coefficient \(\mathrm{R}=-0.98244\). At the confining pressure of 70 MPa,  
\[\sigma=-4.3184\;\mathrm{W}+47.8514, \tag{2}\]  
where \(\sigma\) is the triaxial compressive strength (MPa) of shale; \(\mathrm{W}\) is the moisture content (%); the correlation coefficient \(\mathrm{R}=-0.98284\). At the confining pressure of 80 MPa,  
\[\sigma=-4.5093\;\mathrm{W}+53.1294, \tag{3}\]  
where \(\sigma\) is the triaxial compressive strength (MPa) of shale; \(\mathrm{W}\) is the moisture content (%); the correlation coefficient \(\mathrm{R}=-0.96341\). Equations (1)-(3) indicate that, under the same confining pressure, the triaxial compressive strength of shale is closely related to the water content and the former decreases as the latter increases. The compressive strength decreases linearly with the increase in water content. With the same water content, the triaxial compressive strength of shale rock increases as the confining pressure increases. From the strength fitting curve relationship diagram reflecting different confining pressures and different water contents (as shown in Figure 4), the following can be seen:  
1. When the dry shale rock sample increases from 60 MPa to 80 MPa, the strength increases from 41.659 MPa to 50.491 MPa, an increase of 21.2%. When the saturated shale rock sample increases from 60 MPa to 80 MPa, the strength increases from 9.872 MPa to 11.746 MPa, an increase of 18.98%. It can be seen that the strength of the shale rock clearly increases under the action of high confining pressure;2. When the confining pressure is 60 MPa, the compressive strength of shale with a water content from 0 to 8% decreases from 41.659 MPa to 10.347 MPa, a decrease of 75.16%. When the confining pressure is 70 MPa, the compressive strength of shale with a water content from 0 to 8% decreases from 46.932 MPa to 10.512 MPa, a decrease of 77.60%. When the confining pressure is 80 MPa, the compressive strength of the shale rock decreases from 50.491 MPa to 12.038 MPa, a decrease of 76.16%. It can be seen that hydration significantly degrades the compressive strength of shale. Underground rock formations, especially the deep surrounding rock, are affected by the surrounding ground stress, and a triaxial mechanical characteristic experiment with high confining pressure can reflect the mechanical characteristics of the deep rock. The results of this experiment show that the peak strength of shale (the maximum shear stress that rocks can resist) will be enhanced, and the degree of enhancement with 70 MPa to 80 MPa is slightly greater than that with 60 MPa to 70 MPa. In the dry state, the strength under confining pressures from 60 MPa to 70 MPa and from 70 MPa to 80 MPa is increased by 5 MPa. With the increase in water content, the increase in strength under confining pressure decreases from 60 MPa to 70 MPa, and the strength stops increase with confining pressure when the water content is full. However, when the confining pressure increases from 70 MPa to 80 MPa under each different level of moisture content, the strength increases significantly by about 5 MPa.