# Analysis and Application of Lining Resistance to Water Pressure in Tunnel through Karst Cave
## 5 Discussion  
### Analysis of Damage Characteristics  
In the tunnel construction process, the parallel heading expansion can cause stress redistribution and, thus, cause the tunnel to converge inward; thus, it is important to control and monitor the tunnel deformation during the study of the damage of grouted rock masses and composite surrounding rocks. It is also important to investigate the correlation between acoustic emission energy and damage to the surrounding rock, as a large amount of acoustic emission energy is released whenever there is large damage to the surrounding rock unit. In the numerical calculation model shown in Figures 1 and 12, four monitoring points were set up inside the tunnel, labeled A, B, C, and D. During the calculation, the convergence deformation and acoustic emission energy in the tunnel were monitored and analyzed in the process of sudden water of the composite surrounding rock caused by the increased water pressure in the karst cave, and the displacement was in the positive direction to the right. The results are shown in Figures 23 and 24, respectively. From Figure 23, it can be seen that the unloading caused by the expansion of the parallel heading would cause the release of stress in the surrounding rock. When the parallel heading was first expanded, the four measurement points A, B, C, and D all experienced certain displacements, with the largest displacement at point B near the cavity, which remained the largest displacement until the final destruction. This indicates that, if the convergence deformation on one side of the tunnel construction is larger than the other side in the karst area, attention should be paid to the uneven stress distribution on that side of the site. At this point, a special geological environment was revealed on that side, such as the possible existence of hidden pressure cavities. For the A and C measurement points, due to their distribution being far from the cavity, the cavity water pressure was less affected. After the parallel heading extension, the measurements remained unchanged until the destruction of the grouted stone on the right side of the tunnel. For points B and D, it was obvious that their displacement curves could be roughly divided into three stages:  
Figure 22: Results of field measurements at monitoring sections: (**a**) results of water pressure monitoring at section DK340+300; (**b**) results of rebar stress monitoring at section DK340+300; (**c**) results of earth pressure monitoring at section DK340+300; (**d**) results of water pressure monitoring at section DK340+377; (**e**) results of rebar stress monitoring at section DK340+377; (**f**) results of earth pressure monitoring at section DK340+377. growth period, stabilization period, and dramatic damage period. At the beginning of the parallel heading expansion, the displacement curve of the two points developed rapidly, and the acoustic emission energy accumulated slowly at this time. Then, the displacement of measurement points entered the stable period after reaching the peak, during which the displacement almost did not increase, and almost no acoustic emission energy was generated, indicating that the stone body finally reached a relatively stable state through the continuous redistribution of internal stress. When the water pressure in the cavity reached 0.28 MPa, the displacement of measurement points B and D increased dramatically, and the acoustic emission energy was also generated suddenly and increased rapidly. This stage corresponded to the destruction of the grouted stone body, which gradually dissipated during the destruction process. Finally, when the water pressure in the cavity reached 0.35 MPa, the grouted stone body was completely destroyed. The changes in displacement and acoustic emission energy with the water pressure in the cavern in Figure 24 showed a consistent trend with Figure 23 as a whole.