## 6 Conclusions  
This study focuses on a three-hole parallel subsea tunnel as its research subject. By conducting a single-factor analysis of water inflow, the study employs the analytic hierarchy process and fuzzy evaluation method to establish a comprehensive fuzzy evaluation system for water inflow. The main conclusions are as follows:  
1. Under the condition of three parallel tunnels, the water inflow increases linearly with the rise in permeability coefficient and seawater depth. As the burial depth increases, it exhibits a trend of initially decreasing and then increasing. The water inflow rises with an increase in tunnel spacing, approaching the water inflow of a single-hole tunnel. Conversely, it decreases with an increase in the relative size between the service tunnel and the main tunnel.
2. Under the condition of three parallel holes, there is mutual influence of the seepage field between subsea tunnels, which leads to a decrease in pore water pressure and a decrease in seepage velocity between tunnels. Using a single-hole tunnel model can lead to a higher predicted value of tunnel water inflow.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{5}{c}{**Grades**} & \multicolumn{3}{c}{**Evaluation Matrix**} \\ \cline{2-5}  & **I** & **II** & **III** & **IV** & **V** & \\ \hline Surrounding rock grades & 0 & 0 & 0.3 & 0.7 & 0 \\ Joint fissure development degree & 0 & 0 & 1 & 0 & 0 \\ Rock mass integrity index & 0 & 0 & 0.6 & 0.4 & 0 \\ Weathering degree of rock mass & 0 & 0 & 0.2 & 0.8 & 0 \\ Permeability coefficient & 0 & 0 & 0.22 & 0.78 & 0 \\ Seawater depth & 0 & 0.2 & 0.8 & 0 & 0 \\ Buried depth of tunnel & 0.5 & 0.5 & 0 & 0 & 0 \\ Relative size & 0 & 0 & 1 & 0 & 0 \\ Tunnel spacing & 0 & 1 & 0 & 0 & 0 \\ Drilling and blasting method & 0 & 1 & 0 & 0 & 0 \\ Shield method & 0 & 0 & 0 & 0 & 0 \\ Multicenter circular & 0 & 1 & 0 & 0 & 0 \\ Circular & 0 & 0 & 0 & 0 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 14: Calculation results of the fuzzy matrix of the i indicator layer.  
3. The water inflow evaluation system, constructed based on the fuzzy comprehensive evaluation method, can quantitatively process various influencing factors and classify water inflow grades. Engineering cases have demonstrated that neglecting the mutual influence between tunnels in a single-hole tunnel model can result in an increased water inflow grade. Therefore, in the grading evaluation system for three-hole parallel subsea tunnels, the mutual influence between tunnels should be considered.  
Conceptualization, Z.H. and Z.Z.; methodology, Z.H. and K.Y.; software, K.Y.; validation, Z.H. and K.Y.; formal analysis, Z.H. and K.Y.; data curation, K.Y.; writing--original draft preparation, Z.H. and K.Y.; writing--review and editing, Z.H. and K.Y.; visualization, H.C.; supervision, Z.Z.; funding acquisition, Z.H. and Z.Z. All authors have read and agreed to the published version of the manuscript.  
The research described in this study was financially supported by the General Program of National Natural Science Foundation of China (Grant No.: 51978424), the Innovation Research Group Project of Natural Science Foundation of Hebei Province of China (Grant No.: E2022210078), the S&T Program of Hebei Province in China (Grant No.: 22375416D), and the General Program of Natural Science Foundation of Hebei Province of China (Grant No.: E2022210040).  
Not applicable.  
The data presented in this study are available upon request from the corresponding author.  
The authors declare no conflict of interest.