## 3 Results  
### Mechanical Properties  
#### 3.1.1 Uniaxial Compressive Strength  
The influences of laser-power output, beam diameter and beam moving speed on the uniaxial compressive strength of irradiated rock specimens were investigated, and the results are presented in Figure 3. As shown in Figure 3a, the increased laser-power output results in a significant reduction in the compressive strength. For instance, the compressive strength nonlinearly decreases from 135 MPa of the original specimen without laser irradiation (original specimen) to 93, 83, 69 and 54 MPa, respectively, when the laser-power output increases from 0 W to 400, 600, 800 and 1000 W (diameter and moving speed of laser beam were fixed at 6 mm and 0.5 mm/s, respectively). The compressive strength of the irradiated specimens was reduced by about 31.1%, 38.7%, 48.8% and 60.0%, respectively, compared to that of the original specimen. This may be attributed to the fact that the higher-power laser beam can generate more thermal energy and also result in greater thermal damage to the rock specimens. The uniaxial compressive strength was therefore reduced with an increased laser power. However, the beam diameter had a negative effect on the thermal damage of the irradiated granite specimens, as shown in Figure 3b. The uniaxial compressive strength was increased from 54 to 84 MPa when the laser-beam diameter increased in the range of 6-12 mm (laser power and moving speed of laser beam were fixed at 1000 W and 0.5 mm/s, respectively). The uniaxial compressive strength of the specimen irradiated by a 12 mm laser beam was only reduced by 38% compared to that of the original specimen. The effect of the beam's moving speed on the uniaxial compressive strength is shown in Figure 3c. The uniaxial compressive strength was decreased from 130 to 54 MPa when the laser beam's moving speed was reduced from 4-0.5 mm/s (laser power and beam diameter were fixed at 1000 W and 6 mm, respectively), in which the uniaxial compressive strength was slowly reduced to 101 MPa when the moving speed decreased to 1 mm/s. However, the uniaxial compressive strength of the irradiated specimen was significantly reduced to 54 MPa when the moving speed was reduced further to 0.5 mm/s. Therefore, this suggests that a lower moving speed should be used to achieve greater thermal damage in the granite. As can be seen from the profiles presented in Figure 3, all these influences of laser power, laser-beam diameter and laser-beam moving speed on the uniaxial compressive strength of irradiated specimens are non-linear. The stress-strain curve for the original specimen and irradiated granite with different irradiation parameters are presented in Figure 3d. One can observe that the compression distance of the irradiated specimens is longer than that of the original rock. The strains corresponding to the peak stress of the irradiated specimens are dependent on the irradiation parameters, which are larger than that of the original one. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Variables** & **Mass** & **Length** & **Volume** & **Compressive Strength** \\ \hline Testing accuracy & \(\pm\)0.01 g & \(\pm\)0.02 mm & - & - \\ Uncertainties & 2–5\% & 0.11\% & 0.08\% & 2–5\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Testing accuracy and uncertainty. When the uniaxial compression stress approached the peak, the granite instantaneously fractured accompanied by sounds similar to the rock burst. A considerable number of cracks penetrating from the top to bottom were observed when the uniaxial compression load approached the yield strength of the original rock specimen, as shown in Figures 3d and 4. A typical splitting failure with a slight deformation can be confirmed for the original granite exposed to uniaxial compression. This can contribute to the fact that the granite is a kind of rock with high brittleness.