## 3 Results and Discussion
### Shear Mechanical Properties
#### 3.2.3 Effect of Particle Size on Shear Mechanical Properties  
As demonstrated in Figure 11, the shear strength of coarse granite is considerably lower than that of fine-grained granite when subjected to the same conditions. At a shear angle of 45\({}^{\circ}\), within the range of 25 \({}^{\circ}\)C to 600 \({}^{\circ}\)C, the shear strength of coarse granite under water-cooling shock is measured at 119.28 MPa, 143.10 MPa, 131.89 MPa, 127.04 MPa, 124.23 MPa,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Temperature (\({}^{\circ}\)C)**}} & \multicolumn{4}{c}{**Shear Strength (\%)**} & \multirow{2}{*}{**Cohesion (\%)**} & \multirow{2}{*}{**Internal Friction Angle (\%)**} \\ \cline{3-3} \cline{5-7}  & & **45\({}^{\circ}\)** & & & & & **45\({}^{\circ}\)** \\ \hline \multirow{4}{*}{**High-Temperature**} & 200 & 10.2 & 25.0 & 19.1 & 24.5 & \(-\)4.3 \\  & 300 & 5.1 & 19.9 & \(-\)5.6 & \(-\)1.8 & 6.3 \\
**Temperature** & 400 & 0.9 & 6.4 & \(-\)10.1 & \(-\)8.1 & 5.9 \\
**CooledImpact** & 500 & \(-\)7.0 & \(-\)5.0 & \(-\)22.3 & \(-\)22.6 & 9.5 \\  & 600 & \(-\)12.2 & \(-\)32.5 & \(-\)37.3 & \(-\)42.4 & 14.5 \\ \hline \multirow{4}{*}{**Temperature Liquid-Nitrogen-CooledImpact**} & 200 & 3.3 & 14.0 & 6.0 & 9.1 & \(-\)0.7 \\  & 300 & 2.1 & 5.9 & \(-\)11.9 & \(-\)10.4 & 7.4 \\
**Nitrogen-CooledImpact** & 400 & \(-\)2.3 & 2.5 & \(-\)20.6 & \(-\)18.6 & 10.0 \\  & 500 & \(-\)14.3 & \(-\)10.6 & \(-\)27.5 & \(-\)26.3 & 8.4 \\  & 600 & \(-\)28.2 & \(-\)34.0 & \(-\)43.7 & \(-\)44.8 & 10.7 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Variation in shear characteristics of different types of fine-grained granite with temperature.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Temperature (\({}^{\circ}\)C)**}} & \multicolumn{4}{c}{**Shear Strength (\%)**} & \multirow{2}{*}{**Cohesion (\%)**} & \multirow{2}{*}{**Internal Friction Angle (\%)**} \\ \cline{3-3} \cline{5-7}  & & **45\({}^{\circ}\)** & & & & **45\({}^{\circ}\)** \\ \hline \multirow{4}{*}{**High-Temperature**} & 200 & 10.2 & 25.0 & 19.1 & 24.5 & \(-\)4.3 \\  & 300 & 5.1 & 19.9 & \(-\)5.6 & \(-\)1.8 & 6.3 \\
**TemperatureWater-Cooled** & 400 & 0.9 & 6.4 & \(-\)10.1 & \(-\)8.1 & 5.9 \\  & 500 & \(-\)7.0 & \(-\)5.0 & \(-\)22.3 & \(-\)22.6 & 9.5 \\  & 600 & \(-\)12.2 and 106.27 MPa, respectively. Conversely, the shear strength of fine-grained granite under water-cooling shock is 158.33 MPa, 173.99 MPa, 165.88 MPa, 159.37 MPa, 135.28 MPa, and 113.39 MPa, respectively. This observation indicates that, in variable-angle shear tests, the shear strength of granite decreases as the particle size increases. This phenomenon can be attributed to the fact that coarser granite exhibits poorer internal homogeneity, which in turn affects its overall shear strength [40]. As demonstrated in Figure 12, within the range of 200 \({}^{\circ}\)C to 600 \({}^{\circ}\)C, the cohesion of coarse granite under liquid nitrogen shock is 123.2%, 110.9%, 107.1%, 102.0%, and 80.6%, respectively, and the cohesion of fine granite under liquid nitrogen shock is 109.1%, 89.6%, 81.4%, 73.7%, and 55.2%, respectively. This observation indicates that during the cohesion increase phase, the thermal hardening effect exerts a greater influence on coarse granite. This phenomenon can be attributed to the fact that following thermal treatment, the thermal expansion of the mineral grains in the granite leads to the filling of the original internal pores. Furthermore, coarse granite possesses a higher initial pore rate and a greater proportion of large pores (Figure 13), resulting in a more substantial enhancement in shear strength. Conversely, during the cohesion reduction phase, fine-grained granite exhibits a heightened susceptibility to thermal damage.