## 5 Engineering Application of the Graded Evaluation of Water Inflow  
To validate the applicability of the fuzzy comprehensive evaluation system for water inflow, a case study was conducted using a three-hole parallel subsea tunnel project as an example to assess the grading of water inflow. The basic engineering parameters are shown in Table 13. To explore the mutual influence between tunnels, the grade of water inflow is divided into two situations: (1) considering the mutual influence between tunnels, the evaluation indicators include tunnel geometric characteristics (tunnel spacing and relative size); (2) without the mutual influence between tunnels, the water inflow grade adopts a single-hole tunnel model.  
Considering the mutual influence between tunnels  
The weight of evaluation indicators is first calculated, and the corresponding evaluation matrix is obtained using a trapezoidal membership function. Multiplying the weight of the indicator layer by the corresponding evaluation matrix can obtain the fuzzy matrix of the indicator layer. The specific calculation results are shown in Table 14.  
Based on this, the fuzzy matrix of the water inflow criteria layer of the main tunnel can be obtained in the case of three parallel holes:  
\[R_{1}=\left(\begin{array}{c}A_{1}K_{1}\\ A_{2}K_{2}\\ A_{3}K_{3}\\ A_{4}K_{4}\\ A_{5}K_{5}\end{array}\right)=\left(\begin{array}{cccc}0&0&0.5232&0.4768&0\\ 0.0503&0.0954&0.3287&0.5256&0\\ 0&0.6667&0.3333&0&0\\ 0&0.7500&0&0&0\\ 0&0.6667&0&0&0\end{array}\right)\]  
By substituting \(\mathbf{R_{1}}\) into Equation (5), the evaluation vector \(\mathbf{T_{1}}\) = (0.0143 0.1816 0.3924 0.3840 0) can be obtained. The maximum value in the \(\mathbf{T_{1}}\) vector is 0.3924, which is in the fourth place. Based on the principle of maximum membership, the judgment is made,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline Surrounding rock grades & IV-level & Permeability coefficient (m/d) & 0.093 (m/d) \\ Joint fissure development degree & Developed & Seawater depth (m) & 19 m \\ Rock mass integrity index (\(\mathrm{Kv}\)) & 0.41 & Tunnel burial depth (m) & 35 m \\ Rock weathering degree & Moderately weathered & Relative size & 0.50 \\ Tunnel construction methods & Drilling and blasting method & Tunnel profile shape & Multicenter circular \\ \hline \hline \end{tabular}
\end{table}
Table 13: Engineering parameters.  
Figure 14: Trapezoidal membership function.  
taking into account the mutual influence between tunnels. Under this working condition, the water inflow is level III.  
(2) Not considering the mutual influence between tunnels  
Adopting a single-hole tunnel model, without considering the mutual influence between tunnels, the evaluation indicators remove the geometric features of tunnels (tunnel spacing and relative size) and still use the fuzzy comprehensive evaluation method to grade the water inflow of tunnels under the same conditions, obtaining the fuzzy matrix of the criteria layer:  
\[R_{2}=\left(\begin{array}{cccccc}0&0&0.5232&0.4768&0\\ 0.0503&0.0954&0.3287&0.5256&0\\ 0&0.7500&0&0&0\\ 0&0.6667&0&0&0\end{array}\right)\]  
Substitute \(R_{2}\) into Equation (5) to obtain the evaluation vector \(\mathbf{T_{2}}=\left(0.0151\ 0.1265\ 0.3940\ 0.4268\ 0\right)\). Based on the principle of maximum membership, without considering the mutual influence between tunnels, the water inflow under the same conditions is level IV. Consequently, in certain engineering projects, using a single-hole tunnel seepage model without considering the mutual influences between tunnels may result in overestimating tunnel water inflow, leading to the waste of water-blocking materials.