## 3 Test Results
### Effect of Water on Mechanical Behavior
#### 3.1.2 Water-Weakening Effect on Mechanical Behavior  
Table 3 lists the average value of the mechanical properties (i.e., UCS, elastic modulus and critical strain) obtained from the stress-strain relationships. The UCS is the maximum stress exerted on  
Figure 3: Stress–strain curves of (**a**) sandstone; (**b**) granite; and (**c**) marble under dry and water-saturated conditions.  
specimens, the elastic modulus is the slope of linear portion in the curves, and the critical strain is the strain of specimen at the peak stress. It can be clearly seen that the mechanical parameters of the three rock types decreased under water saturation conditions.  
Figure 4a illustrates that the uniaxial compressive strengths (UCSs) of all three types of rocks were reduced by water. Among the three tested rock types, the sandstone specimen underwent the largest drop in UCS due to water saturation. The average UCS of the dry sandstone specimen was 71.91 MPa. After soaking, the average UCS of the sandstone specimen was reduced to 50.48 MPa. For the granite, the average UCS of the saturated specimen decreased to 119.39 MPa from 123.82 MPa in the dry state. There was a negligible UCS reduction for the marble, indicating that the strength of the marble was not apparently affected by water. Apart from the reduction in the average UCS, the standard deviation of the average UCS also decreased after water saturation. The average UCSs of dry sandstone, granite and marble specimens possessed standard deviations of 0.27, 6.34 and 1.26 MPa, respectively. The UCS standard deviations of saturated sandstone, granite and marble specimens were 0.16, 5.70 and 0.49 MPa, respectively. The tested UCS values were less scattered for saturated rocks compared to dry ones.  
Figure 4b displays the elastic modulus of dry and saturated rocks. The elastic modulus followed a similar weakening trend as UCS. The elastic modulus of all three rock types also decreased after water saturation. The reduction in the elastic modulus of the sandstone was considerable, and that of the granite was relatively minor, while that of the marble was not apparent.  
Figure 4c exhibits the water-induced variation of critical strain. Under saturated condition, the loss in the critical strain was noteworthy for the sandstone compared to the relatively small reductions for the granite and the marble.  
Figure 4: _Cont_.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Rock Type**} & \multirow{2}{*}{**State**} & \(\mathbf{t_{f}}\) & \(\sigma_{c}\) & \(E\) & \(\varepsilon_{c}\) & \(N_{\epsilon}\) \\ \cline{3-7}  & & **/s** & **/MPa** & **/GPa** & **/\%\({}_{\infty}\)** & **/10\({}^{3}\)** \\ \hline \multirow{2}{*}{Sandstone} & Dry & 253.0 & 71.91 & 7.05 & 10.21 & 18.0 \\  & Sat. & 225.9 & 50.48 & 5.52 & 9.16 & 3.7 \\ \hline \multirow{2}{*}{Granite} & Dry & 216.6 & 123.82 & 15.18 & 8.46 & 985.7 \\  & Sat. & 204.8 & 119.39 & 14.34 & 8.32 & 184.5 \\ \hline \multirow{2}{*}{Marble} & Dry & 174.0 & 119.48 & 16.82 & 7.12 & 8.1 \\  & Sat. & 176.5 & 118.77 & 16.78 & 7.08 & 5.9 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Average values of tested data.