## 3 Prediction of Water Gushing in Tunnels  
When tunnels are built through the water-rich fracture structures in igneous rock areas, the amount of water gushing in tunnels will occur in each day of excavation. If the effects of the unexcavated section of the tunnel far from the tunnel face are always taken into account in the calculations, that will cause large calculation errors in the prediction of water gushing. At this point, the combined effect of the areas of water-rich fault fracture zones and construction factors should be considered. The constructed tunnel sections and those, where the aquifer is disturbed, are segmented for the prediction of water gushing [7]. The tunnel is divided into \(N\) sections, and the daily excavation gushing can be set as \(Q\). The calculation formula is given in Equation (9), as follows:  
\[Q=\sum_{n=1}^{N}Q_{n}. \tag{9}\]  
The water gushing in the tunnel is generally derived into two major parts. One is from water released from bedrock fracture water, and the other is from the infiltration of rainfall. They are expressed with reference to Equation (10), as follows:  
\[Q=W_{n(1)}+W_{n(2)}, \tag{10}\]  
where \(Q_{n}\) is the total water gushing in the \(n\)-th section of the tunnel, \(\mathrm{m}^{3}/\mathrm{d}\); \(N\) is the total number of sections of tunnel that have been constructed in a given period and in which the aquifer has been disturbed; \(W_{n(1)}\) is the amount of water released from bedrock fractures, \(\mathrm{m}^{3}/\mathrm{d}\); \(W_{n(2)}\) is the amount of rainfall infiltration, \(\mathrm{m}^{3}/\mathrm{d}\). An example of a tunnel section division is shown in Figure 1.  
When all the water is released from the bedrock fractures, \(W_{n(2)}=0\). Conversely, when the water is infiltrated by rainfall, \(W_{n(1)}=0\). If both of these are deemed to exist, \(W_{n(1)}\) and \(W_{n(2)}\) continue to be determined in the following manner. With a well-developed fracture network and good permeability, the aquifer in the tunnel site area is large in scale, and the storage capacity of water from bedrock fracture  
Figure 1: Example diagram of a tunnel section. is huge. The water released from bedrock fracture can be calculated by the groundwater drainage method. It can be expressed as \(W_{n(1)}\), which is calculated by the following Equation (11) [32; 33]:  
\[W_{n(1)}=\frac{\mu L_{n}H_{n}R_{n}}{T}, \tag{11}\]  
where \(\mu\) is the specific yield of rock; \(L_{n}\) is the length of the \(n\)-th segment, m; \(H_{n}\) is the average thickness of the aquifer above the \(n\)-th tunnel section, m; \(R_{n}\) is the \(n\)-th section of effective radius of water gushing, m; \(T\) is the duration of the water gushing, d.  
Additionally, the replenishment of groundwater in the tunnel site area by rainfall should not be overlooked. Water on the surface will infiltrate into the bedrock along weathered rock layers and fault fracture zones [34; 35]. With regard to the infiltration of rainfall, the effect of rainfall on water gushing can be represented by the following equations:  
\[W_{n(2)}=0.00274\alpha hS, \tag{12}\]  
\[S=2L_{n}R_{n}, \tag{13}\]  
where \(\alpha\) is the coefficient of infiltration; \(h\) is the average annual rainfall, m; \(S\) is the catchment area, m\({}^{2}\). In the previous method of rainfall infiltration, a fixed catchment area is used to calculate the amount of water gushing in the tunnel, which was expressed as the effective radius of water gushing and the length of the tunnel construction. With a fixed total tunnel length, the accuracy of \(R_{n}\) will directly affect the accuracy of \(Q\). However, complex changes will arise in the groundwater seepage field during the long-term construction process. As a result, \(R_{n}\) is constantly changing. The parameter \(\mu\) is a characteristic parameter of the rock mass and \(L_{n}\) is a characteristic parameter of the tunnel. Both of them are relatively stable.