## 7 Conclusions  
This paper investigated the minimum water level requirement for herbaceous plants in alpine meadows, groundwater variation during tunnel construction, waterproofing and drainage parameters, and the discharge limits of tunnel groundwater to protect vegetation. The study employed transplant experiments, numerical simulations of tunnel construction, and calculations of discharge limits. The main conclusions are as follows.  
1. The transplant experiments showed that _Artemisia annua_ grew 4 cm taller than before the experiment when soil moisture content was 30% and groundwater depth was 80 cm. _Stipa_ grew 2.5 cm taller than before the experiment when soil moisture content was 25% and groundwater depth was 80 cm. These increments of growth were the largest. _Artemisia annua_ and _Stipa_ grew well also when groundwater depth was 60 cm. Thus, it is suggested that groundwater depth be controlled between 0.6 m and 0.8 m to protect the normal growth of herbaceous plants.
2. Based on ensuring the normal growth of herbaceous plants around the tunnel, a grouting circle with a thickness of 2 m and a permeability coefficient of 4.9 \(\times\) 10\({}^{-3}\) m/d are proposed. In tunnel construction, groundwater level decline was between 0.02 m and 0.66 m. After the secondary lining construction, the water level gradually recovered. These grouting parameters ensure that the recovery degree of water level can exceed 90%. When these grouting parameters were used, these herbaceous plants were able to normally grow in the construction of Longzang Mountain No. 1 Tunnel.
3. Based on the hydrology, meteorology, and geology information of Longzang Mountain No. 1 Tunnel, the results of the empirical formula calculation showed that when the groundwater discharge limit was 0.2\(\sim\)4.0 m\({}^{3}\)/(m-d), the groundwater level decline was less than 0.8 m. In this situation, herbaceous plants in Qinghai's alpine grasslands were able to normally grow. This research offers guidance and support for managing groundwater discharge during tunnel construction in ecologically fragile areas, such as the Three Rivers Source in Qinghai.  
Conceptualization, X.Z.; methodology, Y.Z.; software, Y.L. and Y.Y.; validation, Y.L.; formal analysis, X.Z.; investigation, Y.Y.; writing--original draft preparation, Y.L. and Y.Y.; writing--review and editing, Y.Z. All authors have read and agreed to the published version of the manuscript.  
This study was funded by the National Key Research & Development Program of China (2021 YFB2600103), and the Natural Science Foundation Chongqing, China (No. CSTB2022 NSCQ-MSX1515).  
Not applicable.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name** & **Tunnel Type** & **Surrounding Rock Type** & **Grouting Thickness/m** & **Grouting Permeability Coefficient/(m/d)** \\ \hline Longzang Mountain & \multirow{2}{*}{Mountain tunnel} & The surrounding rock is & \multirow{2}{*}{2} & \multirow{2}{*}{\(4.9\times 10^{-3}\)} \\ Tunnel No. 1 & & relatively complete & & \\ \hline Yuanliangshan tunnel [36] & Water-rich karst tunnel & Broken surrounding rock & 5 or 8 & \(8.64\times 10^{-4}\) \\ \hline Liaoshan Tunnel [37] & Water-rich karst tunnel & \multirow{2}{*}{\
\begin{tabular}{c} The surrounding rock is \\ relatively complete \\ \end{tabular} } & \multirow{2}{*}{1} & \multirow{2}{*}{/} \\ Guangfu Tunnel [38] & Shallow buried bias & & & \\  & pressure tunnel & & & \\ \hline Cenxi Tunnel [39] & \multirow{2}{*}{
\begin{tabular}{c} Fully weathered \\ granite tunnel \\ \end{tabular} } & \multirow{2}{*}{Broken surrounding rock} & \multirow{2}{*}{6} & \multirow{2}{*}{/} \\ \hline \hline \end{tabular}
\end{table}
Table 4: Grouting parameters for different tunnels.  
Data Availability Statement: The data presented in this study are available upon request from the corresponding author. The data are not publicly available due to privacy.  
The authors declare no conflict of interest.