## 7 Conclusions  
1. The theoretical model and semi-analytical algorithm of the collaborative drainage scheme for a tunnel and parallel edit proposed here can accurately meet the preset drainage boundary conditions in several iterations. The calculation results are consistent with the numerical simulation results, which are suitable for the calculation and analysis of drainage schemes.
2. The drainage volume of the parallel edit negatively correlates with the water pressure at the tunnel boundary with a strong correlation coefficient, and the influence on water pressure is the most significant. The horizontal distance between parallel edit and tunnel has a linear positive correlation with water pressure at the tunnel boundary; however, its influence is less than drainage volume. The water pressure of  
Figure 16: Comparison of fitting results and semi-analytical solution of pressure head on the tunnel crown.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Experiment Number** & \(r_{\text{p}}\)**/m** & \(r_{\text{t}}\)**/m** & \(d_{\text{tw}}\)**/m** & \(S_{\text{h}}\)**/m** & \(S_{\text{v}}\)**/m** & \(\delta_{\text{t}}\) & \(\delta_{\text{p}}\) \\ \hline
1 & 3.0 & 6.0 & 100 & 10 & 0.75 & 0.5657 & 0.3448 \\
2 & 3.0 & 6.5 & 250 & 15 & 1.50 & 0.6946 & 0.4536 \\
3 & 3.0 & 7.0 & 400 & 20 & 2.25 & 0.7565 & 0.4991 \\
4 & 3.0 & 7.5 & 550 & 25 & 3.00 & 0.7957 & 0.5250 \\
5 & 3.5 & 6.0 & 250 & 20 & 3.00 & 0.7082 & 0.4328 \\
6 & 3.5 & 6.5 & 100 & 25 & 2.25 & 0.5617 & 0.2690 \\
7 & 3.5 & 7.0 & 550 & 10 & 1.50 & 0.8082 & 0.5927 \\
8 & 3.5 & 7.5 & 400 & 15 & 0.75 & 0.7461 & 0.5173 \\
9 & 4.0 & 6.0 & 400 & 25 & 1.50 & 0.7820 & 0.4884 \\
10 & 4.0 & 6.5 & 550 & 20 & 0.75 & 0.8196 & 0.5567 \\
11 & 4.0 & 7.0 & 100 & 15 & 3.00 & 0.5447 & 0.3000 \\
12 & 4.0 & 7.5 & 250 & 10 & 2.25 & 0.6731 & 0.4576 \\
13 & 4.5 & 6.0 & 550 & 15 & 2.25 & 0.8339 & 0.5799 \\
14 & 4.5 & 6.5 & 400 & 10 & 3.00 & 0.7716 & 0.5435 \\
15 & 4.5 & 7.0 & 250 & 25 & 0.75 & 0.6850 & 0.4067 \\
16 & 4.5 & 7.5 & 100 & 20 & 1.50 & 0.5371 & 0.2783 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Scheme and results of the orthogonal experiment.  
the lining facing the parallel edit side is significantly less than that on the other side when the parallel edit is collaboratively drained. The smaller the horizontal distance between parallel edit and tunnel, the larger the drainage volume of the parallel edit, and the more significant the inhomogeneity. Therefore, in order to reduce water pressure uniformly and meet the requirements of surrounding rock stability, the horizontal distance between the parallel edit and tunnel should be no less than the tunnel diameter. The height difference between the parallel edit and the tunnel has little effect on the water pressure on the lining; however, it only needs to meet other construction and operation requirements.
* Based on the semi-analytical results, the pressure head formula of tunnel crown fitted by using nonlinear regression theory has a quality fit, which can be used to calculate and analyze the parameters of the collaborative drainage scheme for a tunnel and parallel edit. The formula can also intuitively express the contribution of water pressure release to each parameter.  
Y.X.: conceptualization; X.L.: formal analysis; software; writing--review and editing; C.Y.: data curation, investigation. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Fundamental Research Funds for China Central Universities, grant number 2021 YJS10 and the Scientific Research Project of Hunan Education Department, grant number 20C0842.  
Not applicable.  
Data Availability StatementData are contained within this article.  
The authors declare no conflict of interest.