# Analysis and Application of Lining Resistance to Water Pressure in Tunnel through Karst Cave
## 2 Failure Mode of Grouting in Tunnels Crossing High-Pressure Karst Caves
### Influence of Grouting Range on the Effect of Grouting
#### 3.1.2 Results of Numerical Calculations  
According to the numerical simulation calculation results, the damage pattern diagrams of typical steps were extracted as shown in Figure 13, corresponding to steps 1-1 (0.1 MPa), 2-1 (0.11 MPa), 90-2 (1.0 MPa), 110-1 (1.2 MPa), 210-1 (2.2 MPa), 210-2 (2.2 MPa), and 210-6 (2.2 MPa), and 210-9 (2.2 MPa). Observing the figure, it can be found that, because the initial state of the cavity had 0.1 MPa water pressure, there were circular stress zones distributed before the excavation of the existing parallel heading and around the cavity, and no crack expansion of the composite surrounding rock between the cavity and the parallel heading occurred at this time. After the construction of the existing parallel heading expansion, the original stress balance around the tunnel was broken, and stress redistribution appeared around the tunnel. Furthermore, the composite surrounding rock showed a very obvious stress concentration and finally reached a new stress equilibrium state under the repeated coupling effect of force and flow fields. With the increased water pressure inside the cave, it can be found that a micro-crack had sprouted in the outer layer of the composite surrounding rock of the grouted stone body, and, with the further increase in the stress concentration in the grouted stone body, a macroscopic crack had extended through to the inner layer of the composite surrounding rock body. At this time, the cavity water pressure acted on the surrounding rock through the crack. Then, with the continuous increase in the water pressure in the cavity, the main crack connecting the bottom of the cavity and the bottom of the tunnel arch was extended through. Finally, the whole composite surrounding rock body collapsed to the interior of the tunnel.  
The acoustic emission of the typical loading step obtained from the calculation is shown in Figure 14. As can be seen from the figure, after the parallel heading was just expanded to form the tunnel, the composite surrounding rock structure was intact, and the acoustic emission energy was weak. With the increasing water pressure in the cavity, the acoustic emission energy gradually accumulated. When the water pressure in the cavity rose to 1.0 MPa, the grouted stone body in the outer layer of the composite surrounding rock started to appear as a compression shear unit, and the distribution of the pressurized unit expanded along the cavity toward the tunnel. This feature was reflected in the minimum principal stress diagram as cracks started to appear in the grouted stone body and started to sprout from the inside of the cavity toward the tunnel. Then, as the water pressure in the cavity rose further, the number of compression-shear units on the grouted stone body increased dramatically, reflecting that the structure was being damaged at this time.  
Figure 12: Diagram of the numerical calculation model.  
Eventually, the grouted stone body was damaged, and the water pressure in the cavity acted on the inner layer of the composite surrounding rock body along the fracture of the grouted stone body, which appeared as a tensile-shear damage unit. For the above model, when the water pressure in the cavity reached 2.2 MPa, the surrounding rock body was damaged, and the crack at this time was mainly caused by the tensile-shear damage.