# Research Progress on the Mechanisms and Control Methods of Rockbursts under Water-Rock Interactions
## 3 Research Progress on Water's Impact in Strain-Induced Rockburst Experiments  
### Study of Strain-Induced Rockburst Tendencies under Different Moisture Contents  
To explore how water affects the mechanical characteristics of rocks, [PERSON] [39] carried out uniaxial and true triaxial compression experiments on natural water content (NWC) red sandstone samples, as did saturated water content (SWC) samples. They monitored and recorded the tunnel sidewalls in real time from intact to damaged. These results and data were synthesized to clarify the physico-mechanical how water affects the surrounding hard rock. First, they selected three cylindrical samples and measured their mass (\(m_{1}\)) with natural water content (NWC) using an electronic scale. The dry mass (\(m_{2}\)) of the samples was then obtained by drying the samples in an oven, at 105 \({}^{\circ}\)C for 1 day to eliminate the moisture within the samples and then weigh them. Subsequently, they soaked the dried specimens with water for 2 days to reach saturated water content (SWC) conditions and were weighed for SWC mass (\(m_{3}\)). The test is carried out on the sample for uniaxial compression. Figure 1a shows the stress-strain curves from these tests. \"The stress-axial strain curves for the NWC samples\" exhibited considerable variability, whereas the SWC samples displayed much more uniform curves. This suggests that red sandstone becomes more homogeneous under SWC conditions, with less noticeable changes in physical properties. Compared to uniaxial compression results, \"the strength and modulus of elasticity\" of sandstone decreased under SWC conditions, specifically by 11.2 MPa (11.5% reduction) and 0.8 GPa (4.3% reduction), respectively. This indicates that water presence diminishes both the strength and modulus of elasticity of red sandstone, with strength reductions being more pronounced [61]. Figure 2 illustrates the damage pattern of the sample in the uniaxial compression test. For both moisture content conditions, the rocks are mainly damaged by shear. Samples \(D_{3}\) and \(W_{2}\) showed shear failure along single shear planes, while other samples exhibited shear failure along conjugate shear planes forming an 'X' shape. During the tests, the three NWC cylindrical samples experienced a sudden and rapid stress drop upon reaching peak stress. In contrast, the SWC samples did not show a sudden stress drop at peak stress (Figure 1b). Around the peak stress of the stress-strain curves, there were noticeable fluctuations, but the degree of failure was less severe in the SWC samples compared to the NWC samples. This indicates that, under the NWC condition, red sandstone experienced more severe failure and demonstrated a greater propensity for rockbursts compared to red sandstone in the SWC condition. Next, the researchers performed true triaxial tests on the samples, The loading stresses were recorded and plotted as shown in Figure 3. The result reveals that, during the stepped loading phase, the variation in stress for SWC samples is notably less than that observed in NWC samples. Additionally, the initial stress and maximum vertical stress during the stepped loading phase are higher for SWC samples than for NWC samples. This suggests that the presence of water makes it initially more difficult for macroscopic damage to occur in tunnels. Nevertheless, once damage occurs in saturated hard rock tunnels, even small stresses can contribute to the appearance of significant damage. The researcher observed the damage observed on the side walls of the cube hole specimens prior to the unloading phase. Under triaxial stress conditions, all the holes experienced considerable flaking on the sidewalls that are at a right angle to the direction of the applied upright load. Upon comparing the extent of sidewall damage, it is evident that in the NWC cubic hole specimens, the damage zones along the hole axis were highly variable, with distinct areas of concentrated damage.